maximillianos - 5:17 pm on Apr 26, 2010 (gmt 0)
We had this happen a few months back. Turns out it was a problem with our banner ad network (TribalFusion). They told us one of their IP addresses got on the virus list by mistake. They told us it would be fixed in the next update of the user's anti-virus software.
We said that was not acceptable. We suggested they swap that IP out. They offered no other solution and just kept telling us to re-install their code. We dropped them. It was making us look pretty bad, like we had a virus on our site.
Turns out we make more by running an Adsense image banner there than we did with their ads, so it was a net gain for us, and a big net loss for Tribal... ;-)