Users are getting malware/virus warnings when visiting my forum - what do I do?
 

I am getting a high percentage of users claiming they're getting a malware/virus warning by their security programs when they frequent my forum. I looked through the server and the files, and they're is absolutely nothing out of the ordinary. It doesnt happen all the time, and some are saying when running a no-script plugin on their browser, it has blocked a cross-site scripting (XSS) attack multiple times.

The only outside javascript I'm running on my site is Google Adsense, Google Analytics, OpenX, and Quantcast.

How can I get this resolved? This only seems to be happening with Windows users, and has been hard to duplicate.

Thoughts?