Recently my computer was infected by an I-WORM/Brontok.DN it not a big deal to me however it some kind of annoying.
As a personal preference I enjoy seeing all file extension. After remove the worm all my .exe extension never show. Well it not a big deal but it just for my good practise habit it annoying me.
I spend a few hours to find what cause the problem. I when all the way from Folder Options up to registry key. In the end I found that the worm had install a key call NeverShowExt in HKEY_CLASSES_ROOT/exefile dam I delete this key viola! I got saved.
In this process (hide/seek) I am victorious with pain, I accidentally delete a good windows citizen file which cause my Tab control no longer support XP visual style :( I hope to get it back if I couldn't I have to live with it for a while.