PUM.Optional.ExtSetup is Malwarebytes’ detection name for a potentially unwanted modification (PUM) in the Windows registry where a certain family of adware would create a Scheduled Task called extsetup.
Malwarebytes can modify this registry value data back to its Windows default setting without user interaction.
When 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.