Very useful page with common port numbers used by applications.
The big tip:
Let's say you want to block all AIM connections on your home network so the kids can't AIM?
Simply login your router, go to the Security tab, and under "Filter Port range," type in 5190. And make sure you block both TCP and UDP.
MSN Messenger: 6901 & 6891-6900
YIM: 80 (but don't block port 80 unless you don't want to surf the web)
AIM: 5190 and 443
Edited by yano, 29 April 2006 - 12:49 PM.