Understanding how antivirus software detects malware is essential for informed security decisions. Signature-based detection compares files against known malware fingerprints — fast and accurate for known threats but cannot detect novel malware. Heuristic analysis examines code structure and behavior patterns to identify suspicious characteristics. Behavioral monitoring watches programs as they run and flags dangerous activities. Machine learning models analyze file characteristics to identify novel threats. Cloud-based reputation systems leverage collective intelligence from millions of users for instant verdicts. Modern security suites use multiple detection layers — no single technology is sufficient against today’s sophisticated threats.