Problem is that it is illegal. They sent spies into other camps and recorded other teams, allegedly.
Completely against the spirit of competition and against NFL guidelines.
I'm not sure how much that sort of cheating would help because it would be extremely difficult to learn an entire opponent's play book along with their signals in a week, and then prepare your team to defend against those plays. It seems like a crappy way to gain a small edge by making a ton of work for yourself and your staff.
Might as well just train hard and win the old fashioned way, if you ask me.
If they're found guilty, they should get suspended for a few games.