Had a requirement recently to disable flash on a user by user basis in our published desktop environment, this key wasnt readily available on the internet so here it is for anyone else wishing to do the same:

[HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionExtSettings{D27CDB6E-AE6D-11CF-96B8-444553540000}]
"Flags"=dword:00000001
"Version"="*"