Access controls for source libraries are the features of a library control software package that would protect against unauthorized updating of source code. Access controls are the mechanisms that regulate who can access, modify, or delete the source code stored in the source libraries. Source libraries are the repositories that contain the source code files and their versions. By implementing access controls for source libraries, the library controlsoftware package can prevent unauthorized or malicious users from tampering with the source code and compromising its integrity, security, or functionality1.

The other options are not as effective as access controls for source libraries in protecting against unauthorized updating of source code. Option A, required approvals at each life cycle step, is a good practice but may not be sufficient to prevent unauthorized updates if the approval process is bypassed or compromised. Option B, date and time stamping of source and object code, is a useful feature but may not prevent unauthorized updates if the date and time stamps are altered or ignored. Option D, release-to-release comparison of source code, is a helpful feature but may not prevent unauthorized updates if the comparison results are not reviewed or acted upon.