Blocking Instant Messengers?

Michael Mattes asks: "I have been looking for a set of ports/subnets to block in order to disable instant messengers behind my firewall. While MSN is easy to block, ICQ is a little more difficult and it seems as though Yahoo Messenger is designed to do everything possible to not be blocked. I have been reading more and more articles showing companies choosing to block these tools. It seems irresponsible of Yahoo to leave, what appears to me, no choice but to block their entire domain in this situation. Any help would be appreciated."

Comments

Make people not want to use it

[Brento]

At our office, we just started sniffing packets until we caught people trolling for sex partners in chat rooms. Slip a few transcripts out to your friends in the office, and they'll whip through the rumor mill in no time. It'll only be a matter of days before nobody will be dumb enough to IM anybody at all, knowing that someone could be listening in.