If you're running any Avast anti-virus software (at least Windows versions) it's imperative that you update your Avast program IMMEDIATELY. We recently encountered a problem with the most recent update that was blocking every web site on the internet, stating the site was infected with Malware or a Trojan Horse.
A complete scan of our computers identified HTML files being detected by Avast as "infected", even files from Adobe and Quickbooks. Even "blank" HTML files, which made things even more suspicious.
So, I surmised that the problem had to be with Avast giving false positives, and forced Avast to update the program immediate (definition files were up-to-date). The update program option updated Avast from 5.1 to 6.0 and, lo and behold, everything is running with no problems.
So, if you're running Avast, UPDATE IMMEDIATELY!!!!