Maybe that's because Microsoft & their IE software offer lousy security.

Same issue here with Firefox & Avast - Malware detected.
It's likely not something harmful, probably just a sloppily written script.

 

I'm running the latest update of Firefox (3.6.3) and Avast 4.8, again the latest, and I had no problems at all with Thunderheader.net. I assume that you've made sure you're running the latest of both.

 

Au contraire mon ami! Maximum PC magazine just did a comparison test on AV software and MS Security Essentials (free) was rated as an 8 while Avast only managed a 5. All of the reviews of MS Security Essentials that I have read have been positive.

 

Yes Firefox 3.6.3, but I'm running the latest Avast 5.0.507

 

Yep my Avast Antivirus said it blocked a Malware! Bad website Bad Bad!