Block messengers on the network

Here is one site that list most of the ports and what services use them:

http://www.glocksoft.com/trojan_port.htm

Here are a few links from an old TR article titled "Block those ports!"

http://www.iana.org/assignments/port-numbers

http://www.chebucto.ns.ca/~rakerman/port-table.html

http://tinyurl.com/3e77j

Remove any spaces from the pasted links.

Chas

Easiest way? I don't know about that. Yahoo will search for an open port, so you might find yourself constantly checking, blocking, and checking again forever.

Consider a different approach. Users on the network have determined a need to use messenger. If you meet that need, they won't be bothering with bringing in their own solutions. Most user work arounds exist only because IT has placed some barrier to their work that needs to be worked around. Meeting the need keeps you in the loop to match security requirements with business requirements, and makes you a partner instead of an advisary.