I am not experiencing any problems with malware. Should I be?
Goodness no ... you shouldn't be.
However, it is evident that some people are. It sounds browser related. I normally access with Firefox (17.0.1,) and have now tested again with IE 8, and I use a PC. No errors/warnings for me.
I'm not sure how to contact PW admin, but sure they are aware of issue. I'd be happy to do more troubleshooting end user testing scenarios if it will help.
I doubt any individual thread or user is the culprit. But, somewhere along the line PW server has been infiltrated by some malicious code. This is my best guess at least.