заходим на http://www.icq.com/help/

и видим -

A Message for ICQ Users
a new user from ICQ on your contact list.

As part of the process of upgrading ICQ users to our newest, most advanced version, ICQ6, we have added a new user name to your contact list ''ICQ System''. The newly added user is intended to improve ICQ's line of communication with our users and assure you continue to enjoy talking to everybody, everywhere.