The only commentor here that even gets close is the one who said something about freemasonry. I would add secret societies in general, such as Knights of Malta and Jesuits in there as well. But that's stuff the public dismisses as crazy conspiracy theory and the agencies themselves don't like to talk about...
So tired of being dismissed as cookoo and then a few years later saying "I told you so".
Couple of people use the cambridge 5 as an example. First of all, it was the cambridge 6, and they were triples who were always ultimately loyal to the crown.
The middle men of spying are never allowed to be too good because if they were they would realize the top of their own orgs are the problem. Even the one group that used to be allowed to be good, the analysts, who told truth to power, have been slowly being ousted so it's easier to manufacture intel for whatever geopolitical/strategic purposes those at the top want.
The technological revolution has scared them though because they are afraid of being outed, which is why they are quickening the pace to turn the key of the totalitarian dystopian surveillance society. The information revolution is a threat to the powers that be, which is why we will continue to see nothing but an increase in attack tempo on the internet and it's freedoms.