That doesn't make sense.
Why would security "degenerate"?
Creating programs to break into the security makes more sense or someone of equal or better skill being able to crack it makes sense.
Gradually becoming like someone with less skill over time created the security makes no sense.
I could be wrong, but in RL, you get people of equal or better skill figuring out how to get into cell phones which is why Apple, Google and others consistently resecure the system with better (improved skill & intelligence in game terms) security programs / updates.
Why would someone who isn't up to the level of skill be able to break into the system even after time has passed?
Also, what makes you think a node, once secure, can't ever be cracked after that? Food for thought.