Uh, BitDefender could be the cause of your problem. Check these two sites out...
One from Bit Defender, http://news.bitdefender.com/NW.....issue.html, some problems, but mostly for 64 bit OS's it seems.
Another one, I'm listing it here, http://bitdefender-sucks.blogs.....oblem.html, it is sort of old and it seems it is like your problem, but I would put too much weight on it myself.
Have you checked the settings for Bit Defender? I've never used it, but it might have scan settings and intervals you could adjust? Some A/V's have settings for d/l's, installs (writing of a file), and opens. Many times the OPENS are not really needed. If checked when installed or d/l'ed, and if you had a virus, the memory function would catch it, maybe OPEN isn't really needed. Try changing some settings and see if that helps at least, if you can?
Have you tried contacting Bit Defender on this?