Editing Pseudonym (section)

===Concealing identity===
Pseudonymous authors may still have their various identities linked together through [[stylometry|stylometric]] analysis of their writing style. The precise degree of this unmasking ability and its ultimate potential is uncertain, but the privacy risks are expected to grow with improved analytic techniques and [[text corpora]]. Authors may practice [[adversarial stylometry]] to resist such identification.{{sfn|Gröndahl|Asokan|2020|p=16}}

====Business====
Businesspersons of ethnic minorities in some parts of the world are sometimes advised by an employer to use a pseudonym that is common or acceptable in that area when conducting business, to overcome racial or religious bias.<ref>Robertson, Nan, ''The Girls in the Balcony: Women, Men, and ''The New York Times (N.Y.: Random House, [2nd printing?] 1992 ({{ISBN|0-394-58452-X}})), p. 221. In 1968, one such employer was [[The New York Times]], the affected workers were classified-advertising takers, and the renaming was away from Jewish, Irish, and Italian names to ones "with a [[White Anglo-Saxon Protestant|WASP]] flavor".</ref>

====Criminal activity====
{{see|Identity fraud}}
Criminals may use aliases, [[fictitious business names]], and [[dummy corporations]] ([[corporate shells]]) to hide their identity, or to impersonate other persons or entities in order to commit fraud. Aliases and fictitious business names used for dummy corporations may become so complex that, in the words of ''[[The Washington Post]]'', "getting to the truth requires a walk down a bizarre labyrinth" and multiple government agencies may become involved to uncover the truth.<ref name=RTR>The Ruse That Roared, ''The Washington Post'', 5 November 1995, Richard Leiby, James Lileks</ref> Giving a false name to a law enforcement officer is a crime in many jurisdictions.

====Literature====
[[File:Die junge George Sand.jpg|thumb|right|180px|A young [[George Sand]] (real name "Amantine Lucile Dupin")]]
[[File:William Sydney Porter by doubleday.jpg|thumb|[[O. Henry|William Sydney Porter]], who went by the pen name O. Henry or Olivier Henry, in 1909]]
A [[pen name]] is a pseudonym (sometimes a particular form of the real name) adopted by an [[author]] (or on the author's behalf by their publishers). English usage also includes the French-language phrase ''nom de plume'' (which in French literally means "pen name").<ref>Please note this is an English construction, and the idiomatic French phrase is ''nom de guerre'' discussed [[#Nom de guerre|below]]. See [[nom de plume]] for details.</ref>  

The concept of pseudonymity has a long history. In ancient literature it was common to write in the name of a famous person, not for concealment or with any intention of deceit; in the New Testament, the second letter of Peter is probably such. A more modern example is all of ''[[The Federalist Papers]]'', which were signed by Publius, a pseudonym representing the trio of [[James Madison]], [[Alexander Hamilton]], and [[John Jay]]. The papers were written partially in response to several [[Anti-Federalist Papers]], also written under pseudonyms. As a result of this pseudonymity, historians know that the papers were written by Madison, Hamilton, and Jay, but have not been able to discern with certainty which of the three authored a few of the papers. There are also examples of modern politicians and high-ranking bureaucrats writing under pseudonyms.<ref>{{Cite web|url=https://www.politico.com/story/2016/09/hillary-clinton-emails-fbi-228607|title=Obama used a pseudonym in emails with Clinton, FBI documents reveal|first1=Josh|last1=Gerstein|first2=Nolan D.|last2=Mccaskill|website=[[Politico]]|date=23 September 2016 }}</ref><ref>{{Cite web|url=https://thehill.com/regulation/energy-environment/297255-former-epa-chief-under-fire-for-new-batch-of-richard-windsor-emails|title=Former EPA chief under fire for new batch of "Richard Windsor" emails|first=Dustin|last=Weaver|date=1 May 2013|website=[[The Hill (newspaper)|The Hill]]}}</ref>

Some female authors have used male pen names, in particular in the 19th century, when writing was a highly male-dominated profession. The [[Brontë family|Brontë sisters]] used pen names for their early work, so as not to reveal their gender (see below) and so that local residents would not suspect that the books related to people of their neighbourhood. [[Anne Brontë]]'s ''[[The Tenant of Wildfell Hall]]'' (1848) was published under the name Acton Bell, while [[Charlotte Brontë]] used the name Currer Bell for ''[[Jane Eyre]]'' (1847) and ''[[Shirley (novel)|Shirley]]'' (1849), and [[Emily Brontë]] adopted Ellis Bell as cover for ''[[Wuthering Heights]]'' (1847). Other examples from the nineteenth-century are novelist Mary Ann Evans ([[George Eliot]]) and French writer Amandine Aurore Lucile Dupin ([[George Sand]]). Pseudonyms may also be used due to cultural or organization or political prejudices.

Similarly, some 20th- and 21st-century male romance novelists – a field dominated by women – have used female pen names.<ref name=maleauthors>{{cite news |last=Naughton |first=Julie |title=Yes, Virgil, There Are Men Writing Romance: Focus on Romance 2012 |url=http://www.publishersweekly.com/pw/by-topic/new-titles/adult-announcements/article/52473-yes-virgil-there-are-men-writing-romance-focus-on-romance-2012.html |access-date=6 May 2014 |newspaper=Publishers Weekly |date=1 June 2012}}</ref> A few examples are Brindle Chase, [[Peter O'Donnell]] (as Madeline Brent), [[Christopher Wood (writer)|Christopher Wood]] (as Penny Sutton and Rosie Dixon), and [[Hugh C. Rae]] (as Jessica Sterling).<ref name="maleauthors" />

A pen name may be used if a writer's real name is likely to be confused with the name of another writer or notable individual, or if the real name is deemed unsuitable.

Authors who write both fiction and non-fiction, or in different genres, may use different pen names to avoid confusing their readers. For example, the romance writer [[Nora Roberts]] writes mystery novels under the name [[J. D. Robb]].

In some cases, an author may become better known by his pen name than their real name. Some famous examples of that include Samuel Clemens, writing as [[Mark Twain]], Theodor Geisel, better known as [[Dr. Seuss]], and Eric Arthur Blair ([[George Orwell]]). The British mathematician Charles Dodgson wrote fantasy novels as [[Lewis Carroll]] and mathematical treatises under his own name.

Some authors, such as [[Harold Robbins]], use several literary pseudonyms.<ref>[http://www.trussel.com/books/pseud_r.htm Rubin, Harold Francis (1916–)] {{Webarchive|url=https://web.archive.org/web/20100114202003/http://trussel.com/books/pseud_r.htm |date=14 January 2010 }}, Author Pseudonyms: R. Accessed 27 November 2009.</ref>

Some pen names have been used for long periods, even decades, without the author's true identity being discovered, as with [[Elena Ferrante]] and [[Torsten Krol]].

[[J. K. Rowling|Joanne Rowling]]<ref>{{Cite web| title = J.K. Rowling| access-date = 5 August 2020| date = c. 2019| url = https://www.jkrowling.com/about/}}</ref> published the ''[[Harry Potter]]'' series as J. K. Rowling.<!-- See article for further explanation, keep it simple here --> Rowling also published the [[Cormoran Strike]] series of detective novels including ''[[The Cuckoo's Calling]]'' under the pseudonym Robert Galbraith.

[[Winston Churchill]] wrote as [[Winston Churchill as a writer|Winston S. Churchill]] (from his full surname Spencer Churchill which he did not otherwise use) in an attempt to avoid confusion with an [[Winston Churchill (novelist)|American novelist of the same name]]. The attempt was not wholly successful – the two are still sometimes confused by booksellers.<ref>{{cite web |periodical=The Age, Hosted on Google News |date=19 October 1940|title=Two Winston Churchills |url=https://news.google.com/newspapers?nid=1300&dat=19401019&id=QJZVAAAAIBAJ&pg=4893,3645349 |access-date=25 October 2013}}</ref><ref>{{cite book |title=My Early Life - Related Books |date=11 May 2010 |isbn=978-1-4391-2506-9 |url=https://books.google.com/books?id=n2EK2khQWfsC&q=%22mr.+winston+churchill+makes+haste+to+add%22&pg=PA218 |access-date=25 October 2013|last1=Churchill |first1=Winston |publisher=Simon and Schuster }}</ref>

A pen name may be used specifically to hide the identity of the author, as with [[Exposé (journalism)|exposé]] books about espionage or crime, or explicit erotic fiction. [[Erwin von Busse]] used a pseudonym when he published short stories about sexually charged encounters between men in Germany in 1920.<ref>{{cite book | author = Granand |date= 2022 |title= Berlin Garden of Erotic Delights | publisher= Waterbury Press }}</ref> Some prolific authors adopt a pseudonym to disguise the extent of their published output, e. g. [[Stephen King]] writing as [[Richard Bachman]]. Co-authors may choose to publish under a collective pseudonym, e. g., [[P. J. Tracy]] and [[Perri O'Shaughnessy]]. [[Frederic Dannay]] and [[Manfred Lee]] used the name [[Ellery Queen]] as a pen name for their collaborative works and as the name of their main character.<ref>{{Cite web|url=http://queen.spaceports.com/Whodunit_1.html |title=Whodunit?|website=Ellery Queen, A Website on Deduction|access-date=May 1, 2022}}</ref> [[Asa Earl Carter]], a Southern white segregationist affiliated with the KKK, wrote Western books under a fictional Cherokee persona to imply legitimacy and conceal his history.<ref>{{cite news |last1=Carter |first1=Dan T. |author-link1=Dan T. Carter |title=The Transformation of a Klansman |url=https://www.nytimes.com/1991/10/04/opinion/the-transformation-of-a-klansman.html |access-date=18 May 2020 |work=[[The New York Times]] |date=4 October 1991 |archive-url=https://web.archive.org/web/20180702011359/https://www.nytimes.com/1991/10/04/opinion/the-transformation-of-a-klansman.html?pagewanted=print |archive-date=2 July 2018}}</ref>

A famous case in French literature was [[Romain Gary]]. Already a well-known writer, he started publishing books as Émile Ajar to test whether his new books would be well received on their own merits, without the aid of his established reputation. They were: Émile Ajar, like Romain Gary before him, was awarded the prestigious [[Prix Goncourt]] by a jury unaware that they were the same person. Similarly, TV actor [[Ronnie Barker]] submitted comedy material under the name Gerald Wiley.

A collective pseudonym may represent an entire publishing house, or any contributor to a long-running series, especially with juvenile literature. Examples include [[Watty Piper]], [[Victor Appleton]], [[Erin Hunter]], and Kamiru M. Xhan.

Another use of a pseudonym in literature is to present a story as being written by the fictional characters in the story. The series of novels known as ''[[A Series of Unfortunate Events]]'' are written by [[Daniel Handler]] under the pen name of [[Lemony Snicket]], a character in the series. This applies also to some of the several 18th-century English and American writers who used the name [[Fidelia (pseudonym)|Fidelia]].

An '''anonymity pseudonym''' or [[multiple-use name]] is a name used by many different people to protect anonymity.<ref Name="Home">{{cite book
|title= Mind Invaders: A Reader in Psychic Warfare, Cultural Sabotage, and Semiotic Terrorism
|last= Home
|first= Stewart
|author-link= Stewart Home
|year= 1987
|publisher= Serpent's Tail
|location= Indiana University
|isbn= 1-85242-560-1
|page= 119
|url= https://books.google.com/books?id=xdXfAAAAMAAJ&q=%22Multiple-use+name%22}}</ref> It is a strategy that has been adopted by many unconnected radical groups and by cultural groups, where the construct of personal identity has been criticised. This has led to the idea of the "open pop star", such as [[Monty Cantsin]].{{clarify|date=April 2023}}

====Medicine====
Pseudonyms and [[acronym]]s are often employed in medical research to [[Privacy for research participants|protect subjects' identities]] through a process known as [[de-identification]].

====Science====
{{more|Academic authorship#Anonymous and unclaimed authorship}}

[[Nicolaus Copernicus]] put forward his theory of heliocentrism in the manuscript ''[[Commentariolus]]'' anonymously, in part because of his employment as a law clerk for a [[Roman Catholic|church]]-government organization.<ref>{{cite web |last1=Oxenham |first1=Simon |title=soft question – Pseudonyms of famous mathematicians |url=https://mathoverflow.net/questions/45185/pseudonyms-of-famous-mathematicians |website=MathOverflow |access-date=12 January 2020}}</ref>

[[Sophie Germain]] and [[William Sealy Gosset]] used pseudonyms to publish their work in the field of mathematics – Germain, to avoid rampant 19th&nbsp;century academic [[misogyny]], and Gosset, to avoid revealing brewing practices of his employer, the [[Guinness Brewery]].{{sfn|Case|Leggett|2005|p=39}}<ref>{{cite web |title=soft question – Pseudonyms of famous mathematicians |url=https://mathoverflow.net/questions/45185/pseudonyms-of-famous-mathematicians |website=MathOverflow |access-date=12 January 2020}}</ref>

[[Satoshi Nakamoto]] is a pseudonym of a still unknown author or authors' group behind a [[white paper]] about [[bitcoin]].<ref>{{Cite web|url=https://theweek.com/articles/561540/misidentification-satoshi-nakamoto|title=The misidentification of Satoshi Nakamoto|date=30 June 2015|website=theweek.com|access-date=22 July 2019}}</ref><ref>{{Cite news|url=https://www.bloomberg.com/news/articles/2019-04-23/john-mcafee-vows-to-unmask-crypto-s-satoshi-nakamoto-within-days|title=John McAfee vows to unmask Crypto's Satoshi Nakamoto, then backs off |last=Kharif |first=Olga |date=23 April 2019|work=[[Bloomberg News|Bloomberg]]}}</ref><ref>{{cite magazine |url=https://fortune.com/2015/12/09/bitcoin-satoshi-identity/ |title=Who is Satoshi Nakamoto, Inventor of Bitcoin? It doesn't matter |magazine=Fortune |language=en|access-date=22 July 2019}}</ref><ref>{{cite web |url=https://www.cnbc.com/2017/10/27/bitcoins-origin-story-remains-shrouded-in-mystery-heres-why-it-matters.html |title=Bitcoin's creator may be worth $6&nbsp;billion – but people still don't know who it is |last=Bearman |first=Sophie |date=27 October 2017 |website=[[CNBC]]|language=en |access-date=22 July 2019}}</ref>

===={{anchor|Noms de guerre|Military_and_paramilitary_organizations,_"war_name"}}Military and paramilitary organizations====
{{Expand section|date=April 2025}}
While taking part in military activities, such as fighting in a war, the pseudonym might be known as a [[nom de guerre]]. It is chosen by the person involved in the activity.<ref>{{cite dictionary |url=https://www.merriam-webster.com/dictionary/nom%20de%20guerre |title=nom de guerre |access-date=1 February 2025 |dictionary=[[Merriam-Webster Dictionary]] |publisher=[[Merriam-Webster]]}}</ref><ref>{{cite dictionary |url=https://dictionary.cambridge.org/es/diccionario/ingles/nom-de-guerre |title=nom de guerre |access-date=1 February 2025 |dictionary=[[Cambridge Dictionary]] |publisher=[[Cambridge University Press]]}}</ref>

====Online activity====
Individuals using a computer [[online]] may adopt or be required to use a form of pseudonym known as a "handle" (a term deriving from [[CB slang]]), "[[User (computing)|user]] name", "[[Logging (computer security)|login]] name", "[[Avatar (virtual reality)|avatar]]", or, sometimes, "[[Screen name (computing)|screen name]]", "[[gamertag]]", "IGN ('''I'''n '''G'''ame ('''N'''ick)'''N'''ame)" or "[[nickname]]". On the Internet, [[pseudonymous remailer]]s use [[cryptography]] that achieves persistent pseudonymity, so that two-way communication can be achieved, and reputations can be established, without linking physical [[identity theft|identities]] to their respective pseudonyms. [[Aliasing (computing)|Aliasing]] is the use of multiple names for the same data location.

More sophisticated cryptographic systems, such as anonymous [[digital credential]]s, enable users to communicate pseudonymously (''i.e.'', by identifying themselves by means of pseudonyms). In well-defined abuse cases, a designated authority may be able to revoke the pseudonyms and reveal the individuals' real identity.{{Citation needed|date=June 2013}}

Use of pseudonyms is common among professional [[eSports]] players, despite the fact that many professional games are played on [[LAN]].<ref>{{cite web |url=http://www.ongamers.com/articles/why-esports-needs-to-ditch-online-aliases/1100-205/ |title=Why esports needs to ditch online aliases |first=Taylor |last=Cocke |work=onGamers |date=26 November 2013 |access-date=14 May 2015 |archive-date=18 May 2015 |archive-url=https://web.archive.org/web/20150518101553/http://www.ongamers.com/articles/why-esports-needs-to-ditch-online-aliases/1100-205/  }}</ref>

Pseudonymity has become an important phenomenon on the Internet and other computer networks. In computer networks, pseudonyms possess varying degrees of anonymity,<ref>{{cite journal |last=Froomkin |first=A. Michael |author-link=Michael Froomkin |date=1995 |url=http://www.wm.edu/law/publications/jol/95_96/froomkin.html |title=Anonymity and Its Enemies |volume=1 |journal=Journal of Online Law |at=art. 4 |ssrn=2715621 |archive-url=https://web.archive.org/web/20080525021152/http://www.wm.edu/law/publications/jol/95_96/froomkin.html |archive-date=25 May 2008 }}</ref> ranging from highly linkable ''public pseudonyms'' (the link between the pseudonym and a human being is publicly known or easy to discover), potentially linkable ''non-public pseudonyms'' (the link is known to system operators but is not publicly disclosed), and ''unlinkable pseudonyms'' (the link is not known to system operators and cannot be determined).<ref>Pfitzmann, A., and M. Köhntopp (2000).  "[http://dud.inf.tu-dresden.de/literatur/Anon_Terminology_v0.23.pdf Anonymity, Unobservability, and Pseudonymity: A Proposal for Terminology] {{Webarchive|url=https://web.archive.org/web/20110709035024/http://dud.inf.tu-dresden.de/literatur/Anon_Terminology_v0.23.pdf |date=9 July 2011 }}". In H. Federrath (ed.), ''Anonymity'' (Berlin: Springer-Verlag), pp. 1-9.</ref> For example, true [[anonymous remailer]] enables Internet users to establish unlinkable pseudonyms; those that employ non-public pseudonyms (such as the now-defunct [[Penet remailer]]) are called [[pseudonymous remailer]]s.

The continuum of unlinkability can also be seen, in part, on Wikipedia. Some registered users make no attempt to disguise their real identities (for example, by placing their real name on their user page). The pseudonym of unregistered users is their [[IP address]], which can, in many cases, easily be linked to them. Other registered users prefer to remain anonymous, and do not disclose identifying information. However, in certain cases, {{srlink|Wikipedia:Privacy Policy|Wikipedia's privacy policy}} permits system administrators to consult the server logs to determine the IP address, and perhaps the true name, of a registered user. It is possible, in theory, to create an unlinkable Wikipedia pseudonym by using an [[Open proxy]], a Web server that disguises the user's IP address. But most open proxy addresses are blocked indefinitely due to their frequent use by vandals.  Additionally, Wikipedia's public record of a user's interest areas, writing style, and argumentative positions may still establish an identifiable pattern.<ref>Rao, J.R., and P. Rohatgi (2000). [http://www.freehaven.net/anonbib/cache/rao-pseudonymity.pdf "Can Pseudonyms Really Guarantee Privacy?"] {{Webarchive|url=https://web.archive.org/web/20210121071211/https://www.freehaven.net/anonbib/cache/rao-pseudonymity.pdf |archive-url=https://web.archive.org/web/20041106171132/http://freehaven.net/anonbib/cache/rao-pseudonymity.pdf |archive-date=2004-11-06 |url-status=live |date=21 January 2021 }} Proceedings of the 9th USENIX Security Symposium (Denver, Colorado, 14–17 Aug. 2000).</ref><ref name="Novak Raghavan Tomkins 2004 pp. 30–39">{{cite conference |last1=Novak |first1=Jasmine |last2=Raghavan |first2=Prabhakar |last3=Tomkins |first3=Andrew |title=Proceedings of the 13th conference on World Wide Web - WWW '04 |chapter=Anti-aliasing on the web |publisher=ACM Press |publication-place=New York, New York, USA |date=May 2004 |isbn=978-1-58113-844-3 |doi=10.1145/988672.988678 |pages=30–39 |oclc=327018361 |conference=WWW '04: Proceedings of the 13th international conference on World Wide Web}}</ref>

System operators ([[sysops]]) at sites offering pseudonymity, such as Wikipedia, are not likely to build unlinkability into their systems, as this would render them unable to obtain  information about abusive users quickly enough to stop vandalism and other undesirable behaviors. Law enforcement personnel, fearing an avalanche of illegal behavior, are equally unenthusiastic.<ref>Clarke, Roger (1998). [http://www.anu.edu.au/people/Roger.Clarke/II/ICrimPrev.html "Technological Aspects of Internet Crime Prevention."] {{webarchive|url=https://web.archive.org/web/20080814085625/http://www.anu.edu.au/people/Roger.Clarke/II/ICrimPrev.html |date=14 August 2008 }}  Paper presented at the Australian Institute for Criminology's Conference on Internet Crime ( 16–17 February 1998).</ref> Still, some users and privacy activists like the [[American Civil Liberties Union]] believe that Internet users deserve stronger pseudonymity so that they can protect themselves against identity theft, illegal government surveillance, stalking, and other unwelcome consequences of Internet use (including [[Internet leak|unintentional disclosures of their personal information]] and [[doxing]], as discussed in the next section). Their views are supported by laws in some nations (such as Canada) that guarantee citizens a right to speak using a pseudonym.<ref>{{Cite web|date=20 April 2001|title=EFF Press Release: Federal Court Upholds Online Anonymous Speech in 2TheMart.com case|url=https://www.eff.org/legal/cases/2TheMart_case/20010420_eff_2themart_pr.html|archive-url=https://web.archive.org/web/20061211074611/https://www.eff.org/legal/cases/2TheMart_case/20010420_eff_2themart_pr.html|archive-date=11 December 2006|access-date=1 July 2020}}</ref> This right does not, however, give citizens the right to demand publication of pseudonymous speech on equipment they do not own.

====Confidentiality====
Most Web sites that offer pseudonymity retain information about users. <!-- They  should protect their users from unwanted disclosures of personal information; in other words, they should assure confidentiality (the information is available only to those authorized to have access). COMMENT:  it is not encyclopedic to talk about what web sites should or shouldn't do.  This could be reworded to discuss the benefits of assuring confidentiality (referenced of course), but I do not know enough about the issue to do it. --> These sites are often susceptible to unauthorized intrusions into their non-public database systems. For example, in 2000, a Welsh teenager obtained information about more than 26,000 credit card accounts, including that of Bill Gates.<ref name="The Irish Times 2000">{{cite news |title=Teenagers hack Gates's credit card |newspaper=The Irish Times |date=2000-03-31 |url=https://www.irishtimes.com/business/teenagers-hack-gates-s-credit-card-1.261930 |access-date=2021-02-21}}</ref><ref name="Enos 2000">{{cite web |first=Lori |last=Enos |title=Welsh Teens Arrested for E-Commerce Hack Attacks |website=E-Commerce Times |date=2000-03-27 |url=https://www.ecommercetimes.com/story/2824.html |access-date=2021-02-21}}</ref> In 2003, VISA and MasterCard announced that intruders obtained information about 5.6 million credit cards.<ref>Katayama, F. (2003) [http://www.cnn.com/2003/TECH/02/17/creditcard.hack/ "Hacker accesses 5.6 Million Credit Cards" ''CNN.com:'' Technology (February 18, 2003).] {{Webarchive|url=https://web.archive.org/web/20160304024014/http://www.cnn.com/2003/TECH/02/17/creditcard.hack/ |date=4 March 2016 }}</ref> Sites that offer pseudonymity are also vulnerable to confidentiality breaches. In a study of a Web dating service and a [[pseudonymous remailer]], [[University of Cambridge]] researchers discovered that the systems used by these Web sites to protect user data could be easily compromised, even if the pseudonymous channel is protected by strong encryption. Typically, the protected pseudonymous channel exists within a broader framework in which multiple vulnerabilities exist.<ref>{{cite book | doi = 10.1007/3-540-45496-9_17 | last1 = Clayton | first1 = R. | last2 = Danezis | first2 = G. | last3 = Kuhn | first3 = M. | title = Information Hiding | chapter = Real World Patterns of Failure in Anonymity Systems | year = 2001 | url = http://www.cl.cam.ac.uk/~rnc1/Patterns_of_Failure.pdf | volume = 2137 | pages = 230–244 | series = Lecture Notes in Computer Science | isbn = 978-3-540-42733-9 | citeseerx = 10.1.1.16.7923 }}</ref> Pseudonym users should bear in mind that, given the current state of Web security engineering, their true names may be revealed at any time.

====Online reputations====
Pseudonymity is an important component of the reputation systems found in online auction services (such as [[eBay]]), discussion sites (such as [[Slashdot]]), and collaborative knowledge development sites (such as [[Wikipedia]]). A pseudonymous user who has acquired a favorable reputation gains the trust of other users. When users believe that they will be rewarded by acquiring a favorable reputation, they are more likely to behave in accordance with the site's policies.<ref>[[Peter Kollock|Kollock, P]]. (1999). [http://www.sscnet.ucla.edu/soc/faculty/kollock/papers/online_trust.htm "The Production of Trust in Online Markets."] {{webarchive|url=https://web.archive.org/web/20090226160128/http://www.sscnet.ucla.edu/soc/faculty/kollock/papers/online_trust.htm |date=26 February 2009 }} In E.J. Lawler, M. Macy, S. Thyne, and H.A. Walker (eds.), ''Advances in Group Processes'' (Greenwich, CT: JAI Press).</ref>

If users can obtain new pseudonymous identities freely or at a very low cost, reputation-based systems are vulnerable to whitewashing attacks,<ref>Feldman, M., S. Papadimitriou, and J. Chuang (2004). "Free-Riding and Whitewashing in Peer-to-Peer Systems." Paper presented at SIGCOMM '04 Workshop (Portland, Oregon, 30 Aug. – 3 September 2004).</ref> also called ''serial pseudonymity'', in which abusive users continuously discard their old identities and acquire new ones in order to escape the consequences of their behavior: "On the Internet, nobody knows that yesterday you were a dog, and therefore should be in the doghouse today."<ref name="friedman-resnick">{{cite journal | doi = 10.1162/105864001300122476 | last1 = Friedman | first1 = E. | last2 = Resnick | first2 = P. | year = 2001 | title = The Social Cost of Cheap Pseudonyms | url = http://www.si.umich.edu/~presnick/papers/identifiers/081199.pdf | journal = Journal of Economics and Management Strategy | volume = 10 | issue = 2 | pages = 173–199 | hdl = 2027.42/71559  | archive-url = https://web.archive.org/web/20081123102704/http://www.si.umich.edu/~presnick/papers/identifiers/081199.pdf | archive-date = 23 November 2008 | citeseerx = 10.1.1.30.6376 }}</ref> Users of Internet communities who have been banned only to return with new identities are called [[Internet sock puppet|sock puppets]]. Whitewashing is one specific form of a [[Sybil attack]] on distributed systems.  
[[File:Disqus_comment_quality_by_anonymity.svg|thumb|Comment quality on [[Disqus]] by type<ref name=":0" /><ref name=":1">{{Cite web|last=Rosen|first=Rebecca J.|date=11 January 2012|title=Real Names Don't Make for Better Commenters, but Pseudonyms Do|url=https://www.theatlantic.com/technology/archive/2012/01/real-names-dont-make-for-better-commenters-but-pseudonyms-do/251240/|access-date=1 July 2020|website=[[The Atlantic]]|language=en-US}}</ref>]]

The social cost of cheaply discarded pseudonyms is that experienced users lose confidence in new users,<ref>{{cite journal | doi = 10.1145/276758.276774 | last1 = Johnson | first1 = D.G. | last2 = Miller | first2 = K. | year = 1998 | title = Anonymity, Pseudonymity, and Inescapable Identity on the Net | journal = ACM SIGCAS Computers and Society | volume = 28 | issue = 2| pages = 37–38 }}</ref> and may subject new users to abuse until they establish a good reputation.<ref name="friedman-resnick" /> System operators may need to remind experienced users that most newcomers are well-intentioned (see, for example, {{srlink|Wikipedia:Please do not bite the newcomers|Wikipedia's policy about biting newcomers}}). Concerns have also been expressed about sock puppets exhausting the supply of easily remembered usernames. In addition a recent research paper demonstrated that people behave in a potentially more aggressive manner when using pseudonyms/nicknames (due to the [[online disinhibition effect]]) as opposed to being completely anonymous.<ref name="tsikerdekis">{{Cite conference  | first = Michail  | last = Tsikerdekis  | title = Engineering anonymity to reduce aggression online  | book-title = Proceedings of the IADIS International Conference – Interfaces and Human Computer Interaction  | place = Rome, Italy  | pages = 500–504  | publisher = IADIS – International association for development of the information society  | year = 2011 }}</ref><ref>{{cite journal | author = Tsikerdekis Michail | title = The choice of complete anonymity versus pseudonymity for aggression online. | journal = EMinds International Journal on Human-Computer Interaction | year = 2012 | pages = 35–57 | volume = 2 | issue = 8}}</ref> In contrast, research by the blog comment hosting service [[Disqus]] found pseudonymous users contributed the "highest quantity and quality of comments", where "quality" is based on an aggregate of likes, replies, flags, spam reports, and comment deletions,<ref name=":0">{{cite web|last1=Disqus|title=Pseudonyms drive communities|url=https://disqus.com/research/pseudonyms/|access-date=15 June 2016|archive-url=https://web.archive.org/web/20160516101013/https://disqus.com/research/pseudonyms/|archive-date=16 May 2016}}</ref><ref name=":1" /> and found that users trusted pseudonyms and real names equally.<ref>{{Cite web|last=Roy|first=Steve|date=15 December 2014|title=What's In A Name? Understanding Pseudonyms|url=https://blog.disqus.com/whats-in-a-name-understanding-pseudonyms|access-date=11 July 2020|website=The Disqus Blog|language=en-us}}</ref> 
[[File:HuffPo_comments_reason_words_insults.svg|thumb|Comment types used on [[HuffPost]] using different kinds of anonymity<ref name=":2" />]]
Researchers at the University of Cambridge showed that pseudonymous comments tended to be more substantive and engaged with other users in explanations, justifications, and chains of argument, and less likely to use insults, than either fully anonymous or real name comments.<ref name=":2">{{citation |last1=Fredheim|first1=Rolf|last2=Moore|first2=Alfred|title=Talking Politics Online: How Facebook Generates Clicks But Undermines Discussion|date=4 November 2015|doi=10.2139/ssrn.2686164 |ssrn=2686164}}</ref> Proposals have been made to raise the costs of obtaining new identities, such as by charging a small fee or requiring e-mail confirmation. Academic research has proposed cryptographic methods to pseudonymize social media identities<ref>{{cite conference|first1=John |last1=Maheswaran|first2=Daniel |last2=Jackowitz|first3=Ennan |last3=Zhai|first4=David Isaac |last4=Wolinsky|first5=Bryan |last5=Ford|title=Building Privacy-Preserving Cryptographic Credentials from Federated Online Identities|conference=6th ACM Conference on Data and Application Security and Privacy (CODASPY)|conference-url=https://sites.google.com/site/codaspy20162/|url=https://dedis.cs.yale.edu/dissent/papers/cryptobook.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://dedis.cs.yale.edu/dissent/papers/cryptobook.pdf |archive-date=2022-10-09 |url-status=live|date=9 March 2016}}</ref> or government-issued identities,<ref>{{cite web|title=CanDID: Can-Do Decentralized Identity with Legacy Compatibility, Sybil-Resistance, and Accountability|author=Deepak Maram |author2=Harjasleen Malvai |author3=Fan Zhang |author4=Nerla Jean-Louis |author5=Alexander Frolov |author6=Tyler Kell |author7=Tyrone Lobban |author8=Christine Moy |author9=Ari Juels |author10=Andrew Miller |url=https://eprint.iacr.org/2020/934.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://eprint.iacr.org/2020/934.pdf |archive-date=2022-10-09 |url-status=live|date=28 Sep 2020}}</ref> to accrue and use ''anonymous reputation'' in online forums,<ref>{{cite conference|title=AnonRep: Towards Tracking-Resistant Anonymous Reputation|author=Ennan Zhai |author2=David Isaac Wolinsky |author3=Ruichuan Chen |author4=Ewa Syta |author5=Chao Teng |author6=Bryan Ford |conference=13th USENIX Symposium on Networked Systems Design and Implementation (NSDI '16)|conference-url=https://www.usenix.org/conference/nsdi16|date=18 March 2016|url=https://www.usenix.org/conference/nsdi16/technical-sessions/presentation/zhai}}</ref> or to obtain one-per-person and hence less readily-discardable pseudonyms periodically at physical-world ''pseudonym parties''.<ref>{{cite conference |doi=10.1145/1435497.1435503 |chapter=An Offline Foundation for Online Accountable Pseudonyms |conference=1st Workshop on Social Network Systems – SocialNets '08 |pages=31–6 |date=1 April 2008 |last1=Ford |first1=Bryan |last2=Strauss |first2=Jacob |title=Proceedings of the 1st workshop on Social network systems - Social ''Nets'' '08 |isbn=978-1-60558-124-8 |conference-url=https://dl.acm.org/doi/proceedings/10.1145/1435497|chapter-url=https://dl.acm.org/doi/10.1145/1435497.1435503|citeseerx=10.1.1.156.4099 }}</ref>  Others point out that Wikipedia's success is attributable in large measure to its nearly non-existent initial participation costs.

====Privacy====
People seeking privacy often use pseudonyms to make appointments and reservations.<ref>{{cite web |first1=Harriet |last1=Ryan |first2=Kimi |last2=Yoshino |url=http://www.latimes.com/news/local/la-me-jackson17-2009jul17,0,3782664.story |title=Investigators target Michael Jackson's pseudonyms |work=[[Los Angeles Times]] |date=17 July 2009 |access-date=14 October 2012}}</ref> Those writing to [[advice column]]s in newspapers and magazines may use pseudonyms.<ref>{{cite web |url=https://news.google.co.uk/newspapers?nid=4TOpqqG69KYC&dat=18830407&printsec=frontpage |title=''Toronto Daily Mail'', "Women's Kingdom", "A Delicate Question", April 7, 1883, page 5 |access-date=14 October 2012}}</ref> [[Steve Wozniak]] used a pseudonym when attending the [[University of California, Berkeley]] after co-founding [[Apple Computer]], because "[he] knew [he] wouldn't have time enough to be an A+ student."<ref name="stix19860514">{{cite news | url=https://www.latimes.com/archives/la-xpm-1986-05-14-vw-5389-story.html |title=A UC Berkeley Degree Is Now the Apple of Steve Wozniak's Eye |work=[[Los Angeles Times]]|date=14 May 1986 |access-date=5 January 2015 |author=Stix, Harriet}}</ref>