Stealing Focus

I'm having this annoying problem. Every minute or so, whatever program I have open gets unfocused for some reason, and I have to click inside its screen to reactivate it. For example when I was typing this, my browser window suddenly lost focus for some reason and I was typing in the void, and had to click on the browser window again.

The same thing happens during ET. I'm playing for a while and all a sudden I get the windows mouse pointer, and I'm no longer controlling ET (unfocus just happened again). I have to click to get back to ET and continue playing. Needless to say that this is frustrating.

I don't know what causes this, but I do know that it's frustrating the crap out of me. I think it may be Windows' automatic update feature. Last time after I updated Windows through the automatic update thingy the problem seemed to have gone, but today it's back.

I've never had this happen before, and I'm not running any program in the background that I hadn't running before when this problem didn't happen yet.

Any clues ?

Update: My windows clock in the bottom right corner just disappeared ...
Update: It's back ..