Backdoor.Multi.ZAccess.gen refers to a technology used in rootkit development. It deals with programs crafted to hide in new kernel device object called max+++, which may stand for alternate detection name of the backdoor.
Removal of Backdoor.Multi.ZAccess.gen requires skillful antimalware to properly identify the parasite so as to cover its components hidden in the above object. In the meantime, the remover will definitely be attacked by the aggressive infection. Unless protected, it will be eliminated by the rootkit when making attempt to scan the locations containing its elements.
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