>>>But is activewindow() unique across users?? I don't think so.
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>Hmm. If ActiveWindow is a handle then I'd hope it's unique on a machine... should not matter across machines as long as the temp file is local.
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>>>And of course, a key is only unique for a limited number of cases. E.g. a numeric key of, let's say, 5 positions is not enough if there are potentially more that 99.999 cases.
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>Yep, if they need more than 99,999 files they'd want an extra character... or to use alphanumeric in which case you can get hundreds of billions of filenames in 5 bytes. ;-)

If we're talking about file names, some characters are not valid, and others are effectively duplicates e.g. "A" and "a" are the same because Windows file names aren't case sensitive.

A better estimate is 10 digits 0-9 + 26 alphabetic chars, or 36 total chars.

36^5 is about 60 million.