Most IM programs in use today adapt themselves automatically to work behind a firewall. This includes unsing port 80, 23, or any other available port to get it's message through. Here's a couple of things you can try though.
To block AOL IM you need to block port 5190 and the AIM authentication servers login.oscar.aol.com (current addresses: 64.12.161.185, 64.12.161.153)
Yahoo Messenger doesn't seem to use any standard port but you can try the same thing with their servers at (cs.yahoo.com and scsa.yahoo.com) 216.136.175.226, 216.136.226.209, 216.136.226.210, 216.136.233.132, 216.136.173.172, 216.136.173.179 and 216.136.233.128
MSN Messenger can be blocked with TCP Port 1863 and IP Range 64.4.13.0/24. I don't believe this will block out any web content with MSN, but use with caution.
ICQ can be blocked with ports 4000/UDP, 5190/TCP, and login.icq.com (205.188.179.233, 64.12.200.89)
I've seen this question a hundred times, and it seems as though as soon as you get a working block in, they (the IM demons) update the software and it finds a way around your configs. Your results may vary - and no guaranties from this ol' boy.
If you really want to prevent the use of Instant Messaging apps, the only sure way is to lock down the workstation to the point that they can no longer be loaded.
Bob
