A customer had a problem with the Disk Cleanup wizard. The customer liaison explained:

The customer would like to know what locations the Disk Cleanup wizard removes files from. The custom is running Application Q. They had a previous incident where they incurred significant downtime because the Disk Cleanup wizard deleted files from C:\Windows\Installer and C:\Temp that caused their application to stop working. When will the Disk Cleanup Wizard remove a Windows update?

Okay, we can talk about how the cleanup of outdated Windows updates works, but holy crap did you say that Application Q stores critical information in the C:\Temp directory?

You cannot assume that any files in the Temp directory will exist for any significant length of time. The name Temp stands for Temporary. Temporary means not permanent. If your application puts critical files in the Temp directory, then it is just asking for trouble.

If you need a permanent place to store your critical information, try a subdirectory of the Local Application Data directory.

Okay, going back to the questions about Windows updates: The Disk Cleanup Wizard removes up a Windows update if it has been superseded by another update. For example, there may be a roll-up update that includes the original update.

But I doubt that’s what made Application Q stop working. I bet it’s assuming that files in a temporary directory have permanent storage duration.