Answer:
C. Address Resolution Protocol (ARP) poisoning.
Explanation:
An antivirus signature file is a program written to describe and remedy a group of identified malware attacks, to prevent future attacks from the described malicious softwares. It is constantly updated to identify more malicious softwares.
A network access protocol (NAC) is used to implement access control on a network, collaborating with other protocols like ARP and unifying antiviruses, intrusion detection and vulnerability assessment.
When the virus signature file is out of date, the NAC allows a new malware, the antivirus can not identify, to access the network through ARP poisoning.
