PUM.Optional.Userinit is Malwarebytes detection name for a potentially unwanted modification in the Windows registry that could provide a startup location for malware.
A filename would be added to the following registry value data to gain persistence:
a change would be made to the value:
Files called from this location will be triggered shortly before the logon screen.
Malwarebytes can modify this registry value data back to its Windows default setting without user interaction.
When a PUM is detected on your computer, Malwarebytes for Windows does not know if it was authorized. Optimization software, malware, and Potentially Unwanted Programs (PUPs) are known to make these types of changes, hence they are regarded as potentially unwanted.
To have Malwarebytes for Windows ignore a PUM, you must add the PUM as an exclusion.
When a PUM is excluded, Malwarebytes for Windows does not detect the PUM during scans or Real-Time Protection.