I have heard of this happening! Chances of it being this, though are quite slim.
It happens when you try to run a certain version of an Unreal Tournament cheat; one which costs 50 Euros to buy, and is tied to your machine number. It is called 'Helios Hook', or something like that. Try to run it on any other machine and it changes these extensions.
I also believe the w32.supernova does this., which is more likely.