Signature-based anti-malware software is considered what type of security countermeasure?

Signature-based anti-malware software is classified as a reactive security countermeasure. This type of software operates by scanning files and programs for known malware signatures that have been previously identified and documented. When a match is found, it indicates that the software has identified a potential security threat that already exists on the system.

The key aspect of reactive security measures is that they rely on prior knowledge of threats. Signature-based solutions do not actively prevent malware from entering a system; instead, they react to threats that have already penetrated the defenses. This typically involves alerting the user to the presence of malware, quarantining infected files, or removing those files to mitigate any potential damage.

In contrast, proactive measures are designed to anticipate and prevent attacks before they occur, while preventive solutions focus on blocking threats proactively. Detective measures look for and identify existing threats without necessarily stopping them. Therefore, while signature-based anti-malware can have elements of other categories, its primary function as a reaction to detected threats solidifies its classification as a reactive countermeasure.