If you remember the foofaraw about the ten Russian sleeper agents who were in the news earlier this year, Strategy Page says they were actually unmasked long before it became public knowledge:
According to Russian officials, the ten Russian spies arrested in the United States last June were betrayed by a Russian espionage official (identified only as “colonel Shcherbakov”) in the SVR (Russian CIA). The U.S. claimed they had been watching the ten sleepers for several years, which may indicate that Shcherbakov has revealed a lot more if he was on the American payroll all that time. Shcherbakov was in charge of the SVR sleeper cell operation. The Russians use military ranks in the police and intelligence services, and colonels are middle-management. There is political pressure to on the head of SVR to resign, indicating that the damage was greater than anyone wants to admit.
Last July, after Shcherbakov was safely in the U.S., American and Russian officials conducted a spy swap in Vienna, Austria. This was the largest such swap since the Cold War. Russia pardoned and freed four Russians, including two former intel officers who had revealed the identities of numerous Russian agents in the West. These two are believed to have more information and insights of value. The U.S. released the ten Russians who had, for the last decade, been trying to pass themselves off as Americans, and operate as “illegals” (spies without diplomatic cover and protection). As part of the deal, the ten Russians had to admit their guilt. The FBI said that they caught on to this bunch early on, and have been watching them for years, trying to obtain more information on how Russian espionage operate in the United States. The FBI finally arrested these ten when it became apparent that the Russians had detected that they were being watched. Or because colonel Shcherbakov believed his SVR bosses were on to him, or because the colonel believed it was time to retire to that secret condo in the United States. Russian government officials are indicating that SVR assassins have been sent to kill Shcherbakov.
Some have speculated that these agents were actually just a cover for “real” sleeper agents who were doing actual espionage work — it’s as viable an explanation as the SVR deliberately placing ineffective agents.