Recently my wife's computer was infected with the Antivirus Security Pro malware. Her computer had a current version of Zonealarm Extreme Security, but, somehow, that failed to prevent the infection.
After trying various approaches, the one thing that worked was to down load Windows Defender as a stand-alone onto a memory stick (or CD). Boot from the memory stick, and let WD do it's thing. Her computer has Win8.
It would be nice if ZA had a similar capability.