Editing ICQ (section)

==UIN==
ICQ users were identified and distinguished from one another by UIN, or User Identification Numbers, distributed in sequential order. The UIN was invented by [[Mirabilis (company)|Mirabilis]], as the user name assigned to each user upon registration. Issued UINs started at '100,000' (6 digits) and every user received a UIN when first registering with ICQ. As of ICQ6 users were also able to log in using the specific [[e-mail]] address they associated with their UIN during the initial registration process.
Unlike other instant messaging software or [[web application]]s, on ICQ the only permanent user info was the UIN, although it was possible to search for other users using their associated e-mail address or any other detail they made public by updating it in their account's public profile. In addition the user could change all of his or her personal information, including [[User (computing)|screen name]] and e-mail address, without having to re-register. Since 2000, ICQ and [[AOL Instant Messenger|AIM]] users were able to add each other to their contact list without the need for any external clients. As a response to UIN theft or sale of attractive UINs, ICQ started to store email addresses previously associated with a UIN.<ref>{{Cite web|url=http://www.icq.com/register/email_attach.php|archiveurl=https://web.archive.org/web/20060209025659/http://www.icq.com/register/email_attach.php|url-status=dead|title=icq.com|archivedate=February 9, 2006}}</ref> As such UINs that are stolen could sometimes be reclaimed, if a valid primary email address was entered into the user profile.