This is because NSA has two roles: eavesdropping on foreign adversaries, and protecting our internal systems from adversaries. Under the first role, they might introduce an exploit known only to themselves. Under the second, they help protect US systems from exploits known to others.
The other side of that coin is the NSA developing SELinux
This is because NSA has two roles: eavesdropping on foreign adversaries, and protecting our internal systems from adversaries. Under the first role, they might introduce an exploit known only to themselves. Under the second, they help protect US systems from exploits known to others.