it is not a actuall detection..
PUM = Possible Unwanted Modification...
eksample, malwarebytes detect that your firewall is turned off...
so it sort of ask you, did you do it? or was it malware that did it.... malwarebytes does not know.
avast does not scan for PUM. but it can scan for PUP
PUP = not a virus / Possible Unwanted Program....again you need to know what the program is and what to do
PUP scan is default off.... only default on in boot scan