Well you know the link to your own site. It happens when I try to log in.
Hasn't happened on any other sites or forums. Oddly both sites were it happens are security forums.
I don't want to mislead you but the only program I've installed recently is "Karen's directory Printer" I researched it first and it seemed OK & I downloaded it from Major Geeks site so should be fine. Just adding clues.
Here is the link to the PC Tools site. It only happens when to hit the submit button to enter a post.
hxxp://www.pctools.com/forum/
Other things I tried:
1. I uninstalled & reinstalled Avast.-no change
2. boot scan--clean no change
3. complete scan with Avast, SD, threatfire, all in regular mode and in Safe Mode---clean no change
4. Scan with march "windows malicious software removal tool"
5. Windows right up to date.
6. PC Tools firewall Plus