Make sure that Zone Alarm is up to date.

Get AdAware6.0 from Lavasoft update and run it.

Get SpyBot Search & Destroy, update and run it.

I have written a couple of tutorials on additional security measures...........have a look and try some.

Panda and PC-Cillin (Trend Micro) are amongst some firms that offer online malware scanning, They can be worth a try, as not all AVs find the same thing at any given point in time.

You must be using some sort of P2P software for your chatroom?

Please go to http://www.bitdefender.com and look in the free downloads section. They do protection tools for a variety of chatroom applications.

Good Luck