How does it work?
It's simple. When you install ICQ, the program asks you to register at a server, which is connected to a broad network of servers spanning the Internet. At the time of registration, you receive a unique ICQ number, also known as a UIN (Universal Internet Number). In addition, ICQ gives you the option of entering personal information along with your ICQ#. This allows other ICQ users to recognize you when you log on. Once you've registered, you can compile a selected list of friends and associates.
ICQ uses this list to find your friends for you. Meanwhile, ICQ waits quietly in the background without interrupting any other applications in use. As soon as you log onto the Internet, ICQ automatically detects the Internet connection, announces your presence to the Internet community and alerts you when friends sign on or off.
Once you know who's on, all it takes is a click of an icon to initiate chat, implement URL transfers, send messages, exchange files, or launch any external peer-to-peer applications.