Check-in to development source control repository first.
Use separate (pre-)release build repository to build alpha, beta, RC and release versions from there
Transfer development repository -> (pre-)release build repository only after review, for example using Project Compare Tool (see: Project Compare Tool)
Unauthorized access to the source code.
Countermeasures
Description
Technical
Store source code encrypted using software protection (see: Software-Protection)
Organizational
Use IT security management system (e.g., according to ISO 27001).