How do I stop .dmgs from automatically mounting? I'm trying to find the best means of stopping dmg files mounting in OS X 10.6.  I was shown a system where 'no mountable filesystem,' would pop up whenever a user tried to mount a dmg but I can't recall how it was achieved.  I'm currently using parental controls but it keeps getting circumvented.  Any help appreciated.
As Administrator user, remove read access from /System/Library/CoreServices/DiskImageMounter.app (and /Applications/Utilities/Disk Utility.app to be on the safe side) for "Everyone" (in the Get Info dialog in the Finder).