What is a primary feature of anti-virus software?

A primary feature of anti-virus software is to compare files against known virus definitions. This process is essential for identifying and mitigating threats posed by malicious software. Anti-virus programs maintain an up-to-date database of virus signatures—unique patterns or codes associated with known malware. When a file is accessed, the software scans it and checks for matches against these signatures. If a match is found, the software can take action, such as deleting or quarantining the file to prevent infection and further spread of the malware.

In this context, when considering the other options, encrypting files pertains to protecting data confidentiality, which is not the primary function of anti-virus software. Monitoring network traffic relates more to intrusion detection systems or firewalls, which focus on observing and analyzing data moving across networks. Updating the operating system is crucial for security but is not a function performed by anti-virus software; rather, it is typically managed by the operating system itself.