Having not added any new applications imagine my fear on getting the dreaded blue screen when I turned my PC on. The culrit was identified as Zonealarm's vsdatant.sys file. I tried searching the internet for actions to take but few were of much practical help to me. I then decided to re-install my Zonealarm Security suite as a NEW installation instead of an upgrade and this appeared to do the trick, at least so far. I still do not know however what caused it anybody with any ideas would be appreciated. My system is a Dell Dimension 9150 desktop PC running windows XP sp2.