ICQ - UIN

ICQ users are identified by numbers called UIN, distributed in sequential order. The UIN was first invented by Mirabilis, as the user name assigned to each user upon registration. The meaning is either Universal Internet Number or Unified Identification Number. Issued UINs started at number 10000 (5 digits) and every user receives a UIN when first registering to ICQ. As of ICQ6, users are also able to log in using the specific e-mail address they associated with their UIN during the registration process. Unlike other instant messaging software or web applications, on ICQ the only permanent user info is the UIN, although it is possible to search for other users using their associated e-mail address or any other detail they have made public (by updating it in the public profile). In addition, the user can change all of his or her personal information, including screen name and e-mail address, without having to re-register. Since 2000, ICQ and AIM users are 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 to a UIN. As such, UINs that are stolen can sometimes be reclaimed. This applies only if (since 1999 and onwards) a valid primary email address was entered into the user profile.