Installer integrity means verifying that a software installer is unchanged, authentic, and still matches the trusted release. These checks usually rely on hashes, digital signatures, certificate validation, or controlled distribution paths. If any of those checks fail, the file may have been altered, replaced, or repackaged by an attacker.
This matters because installers are high-value delivery points: users often run them with elevated privileges and trust them more than ordinary downloads. In real attacks, adversaries may compromise a server or update channel and serve a malicious installer that looks legitimate but drops malware instead of the intended software. Defenders use signed packages, checksum verification, secure mirrors, and endpoint monitoring for unexpected installer hashes or file replacements. In incident response, checking installer integrity helps determine whether a compromise spread through trusted software delivery rather than a single infected machine.