ICQ is an acronym for “I-Seek-You.”
ICQ is an online chat system owned by America Online, Inc. ICQ sessions between individuals can run for hours or days at a time during which these individuals often will have several discrete conversations separated by breaks in time when there is no communication. Each person participating in ICQ chat is assigned a unique ICQ number eight-digit number that remains assigned to them until such time as they abandon that number; the number may or may thereafter be recycled and assigned out to another person.
ICQ has been subject of several cyberattacks that allowed one person to impersonate someone else and to decrypt encrypted traffic. An attacker would initiate these attacks by going to a chat room and finding two people that are friends. The attacker then pretends to be a friend and sends them a Trojan horse via ICQ.