Turned off Microsoft Security Essentials..............

Stable as a ....... erm..... stable thing.

Suggest others do that if they havnt - not ideal, but hey.... you get to play.

can you elaborate? what issues did it solve? i already have MSE set to ignore my entire steam directory...

Sorry - i had random crash issues - about every 5-10 minutes i would simply be dumped to desktop. No log etc.
It got worse and would happen every minute maybe before i realised id left MSE running - so turned it off, started a game and was stable for the duration. Sadly had to go shop, but now here for the night so of course will update should anything untoward happen again.