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I think CCleaner uses it for the installers, however right clicking the installers and looking at the properties doesn't really reveal anything. It's the same with the Revo Uninstaller setup file.
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CCleaner would clean out that Temp folder location.
It's probably just NSIS as the folder name itself is a dead giveaway with "~nsu.tmp", and the Au_.exe I've noticed tons of times before. Allot of installers/uninstallers do that however, even Inno Setup.
most modern install files are made with nsis. Again as stated as au.tmp is in the temp folder it is a temporary file and should be safe to clean. . . probably some installer was not compiled correctly and did not cleanup after. I guess you could looked at the modified date and maybe irk out which installer left it.
or just let it delete
probably some installer was not compiled correctly and did not cleanup after.
Also some may actually need a reboot but if running on XP or newer may not ask for one - well I've noticed that a few times.