Hi,
Was pdf-gen./malware.gen in chest and genuine viruses. Scanned with malware bytes found the same viruses in the registry & system restore and found out it altered IE8 settings to no protection!. Googled about this (virut variant) managed all day to clear this up XP SP3 fully patched and avast v6 latest version on that computer. Did this long run command to fix windows update and security centre within xp. Now stable and clean.
Annoying these pdf trojans though! you could be hit on any web page. Recently had system tool 2011 on another computer, same type of variant.