Some malware avoids infecting the system twice by looking for predefined markers. For instance, if a particular process, registry key or mutex object is present on the host, such malicious software will assume that another instance of itself is already active and terminate before causing further harm. We could decrease the likelihood of infection by preemptively creating markers known to be associated with malware.
more here.........https://zeltser.com/malware-immunization-infection-markers/
more here.........https://zeltser.com/malware-immunization-infection-markers/