A malware signature is a unique pattern, sequence of bytes, or code snippet extracted from a known malicious software sample. Antivirus and cybersecurity tools use these signatures to detect and block specific malware by scanning files and programs for matching patterns. While signature-based detection is effective against known threats, it may not identify new or modified malware variants. Therefore, security systems often combine signature-based methods with heuristic and behavioral analysis to improve detection rates and protect against evolving cyber threats.