Not quite sure which forum to post this in 'security' 'tips n tweaks' or 'applications' (I guess it's a bit of all 3)
 
Anyhow... Yesterday the file associations for .exe files went missing from explorer. I couldn't find anything wrong with the system (no unknown processes, did a full scan with an uptodate virus / adware scanner etc...)
 
The problem was fairly easy to correct (just replace the 'exefile' entry in the .exe key in HKEY_CLASSES_ROOT. I just thought it was a fluke by a misbehaving program (although this is an almost fresh set up, and as such all the apps installed are tried and tested).
 
Today I boot up and find .bat's and .com's are gone (repeat 'repair' actions). What on earth is going on?? Once I can discount but twice, something fishy is going on. Nobody else has access to this machine (nobody knows the admin password or even uses it aside me), and the network is barred from the net via a hardware based firewall.
 
Can anyone help me get to the bottom of this?
 
Windows NT4 SP6a (IE 6 SP1 +shell update)