istealer doesnt even work for like the umm ssomething it says not liocened or something
in case that you have ESET security, it will delete virus even when its not running, best thing you can do is create virtual OS using vmware or MS virtual pc and do all naughty stuff there
ESET is boss like that... and go with what House said
Maybe you've installed some sort of windows anti-virus? check your installed program list
Why would that happen? ;P