I was able to successfully block a variety of instant messenger applications thruogh a combination of GPOs and blocked domain sites for a client of mine. They use Windows 2003 Small Business Edition and a Netgear Rangemax Wireless Gigabit Router WNR3500 (one of the latest models).
Unfortunately, I couldn't figure out how to block the Yahoo messenger within the Yahoo email site, without blocking complete access to Yahoo email (blocking TCP port 443 will block acccess to Yahoo email)
I've done extensive research for the past few days, and I just couldn't find a solution to this problem.
Any help would be really appreciated. Thank you so much.