While politics is the world’s oldest profession (prostitution spun off from it as the second and more honest profession that actually provided real service for the money), a good case can be made for spying being the third oldest profession. Humans have done it since the beginning of civilization. That said, those who have done it were (and are) rarely seen as good people. Sometimes with very good reason. There’s a book or three in that statement.
I’ve written a bit before about Agent Farewell and his critical role in bringing down the Soviet Union. The game of cat and mouse, recruiting sources/operatives/etc. continues today, even though the U.S. really sort of sucks at it. Both recruiting and security/long-term operations. Our HUMINT efforts are nowhere near what they should be thanks to the feckless peanut. What little we do have? Between double agents and poor security, networks in China and elsewhere have been rolled up over the last few years.
Which brings me to two articles you should read. The first is from John Sexton at HotAir, and looks at a Russian penetration of German intelligence. The second is an article recommended to me on Twitter by Richard Lowe, that deals with the growing scandal of a top FBI agent who turned.
Keep in mind Russia has never stopped its efforts, and Chinese operations in the U.S. are positively staggering. The two articles linked are just the topmost tip of the iceberg.