Closing files that don’t belong to you is a terrible idea. Handles get reused immediately, so there is a high probability that a program that was previously writing to its own file will suddenly find itself writing to a completely unrelated file. So *Shut is a bad idea, but difficult to invoke accidentally.

However, CLOSE#0 is very easy to do unintentionally. As OS_Find can return a file handle of zero if it fails to open the requested file, a badly written program can end up doing CLOSE#0 by mistake.

Either way, it is to be avoided if you want to escape file corruption. !CloseHook is a solution. Whether in the Desktop, in a TaskWindow, or at the command line or a single-tasking program, CloseHook provides a confirmation before allowing *Shut or CLOSE#0 to proceed. If permission is not given, the program carries on none the wiser. Stick it in your Boot sequence and forget about it... until it saves your bacon. Many thanks to Martin Avison for the idea.