I’m sure MSN messenger like other messengers out there will switch ports if you attempt to block it’s specific port. You’ll probably have to block external access to the messenger servers at MSN. To do that, isolate a test while creating a debugging log file on the PIX (low network traffic makes this much easier). See what IP addresses MSN Messenger is trying to connect to and use those hosts as the IP address to block access to with your acl. Watch out, there’s probably more than one Messenger server so you’ll have to be patient and keep trying as you block one, then the next, then the next, etc.
