to Darwin_Koala also:
I do not allow users "free access to the C:\programs" folders .. they have free access to their own folder (C:\ctrlaltdel\ is one of them, the rest are also in the root directory, and also named for the individual user). As for updating, I install to the C:\mircversion folder (example: c:\mirc635) and simply copy/paste the new .exe file and help files (as necessary).
I fail to see how this is "bad practice" .. I have total control over the scripts in each folder (not all the same), which keeps them from loading scripts they don't need.
If they were in "one install" the scripts would be available for everyone which in MY opinion would be a security risk since I personally use scripts that the others have no business even seeing.
To each his own, I guess.