Non-free software is made by companies which are subject to national regulations. The "give us a backdoor to your security product or it will get very ugly for

Non-free software is made by companies which are subject to national regulations. The "give us a backdoor to your security product or it will get very ugly for you." kind of regulation. Being non-free, those back doors are much harder to find than in Open Source SW. Even if you found a back door, publishing it would be risky, as the SW company would immediately sue you for violating the EULA.