Code integrity is the assurance that software is exactly what it is supposed to be: complete, unaltered, and free from transcription or tampering errors. In practice, it means the source code, build artifacts, and deployed binaries match trusted versions and have not been changed without approval. This matters because even a small edit can introduce bugs, backdoors, or unsafe behavior.
In cyber security, code integrity is protected with hashes, digital signatures, signed updates, reproducible builds, and strict change control. Attackers try to break it by modifying source in a repository, injecting code into a build pipeline, or patching executables after release. Defenders check integrity to catch supply-chain compromise, unauthorized hotfixes, and corrupted archives. For text-based software, like old program listings, a single missing character or altered line can change how the code runs, which is why exact preservation is so important.