

These issues might require users to reinstall the operating system due to instability. However, serious issues can occur when you modify the registry incorrectly using these types of utilities. "Some products such as registry cleaning utilities suggest that the registry needs regular maintenance or cleaning. This page does not provide any information as to why Microsoft is now classifying CCleaner as a PUP/PUA, but Microsoft has stated that they do not support Registry cleaners and that they should not be used.

In a new threat entry added today to the Microsoft Security Intelligence site, Microsoft is now classifying CCleaner as a PUA:Win32/CCleaner threat. This ban was due to Microsoft's general stance that Registry cleaners and system optimizers can do more harm than good on Windows systems.
