“If a politician or businessman knows that the K.G.B. can publish embarrassing photos of him or send them to his wife, this person is very easy to control,” Mr. Ehasalu said in a telephone interview. Businessmen who fell into this trap, he said, “all went back home and said life in the Soviet Union was fine and that Finland should make more business with the Soviets.”

An early victim of kompromat was Joseph Alsop, an influential American newspaper columnist who, during a 1957 visit to Moscow, fell into a gay “honey trap” set by the K.G.B., which filmed his encounter with a young Russian man at his hotel.

In his own account of how two K.G.B. officers stormed into his room shortly after he finished having sex, Mr. Alsop said he was told that there were photographs of “the act” and that he needed “to help them a little if they are going to help me.” He informed the American Embassy and hastily left the Soviet Union.

Russia, unlike Estonia, has hardly turned its back on Soviet-era methods. The F.S.B., the successor agency to the K.G.B., lost much of its influence in the early 1990s, but has reasserted itself forcefully since Vladimir V. Putin took power 16 years ago.

Before becoming president, Mr. Putin played a prominent role in a particularly successful kompromat operation. As head of the F.S.B. in 1997, he won the trust of President Boris Yeltsin by helping destroy the career of Russia’s prosecutor general, Yury Skuratov. After starting an investigation into Kremlin corruption, the prosecutor was disgraced on national television by the broadcast of a video that showed a man who looked like him in bed with two young women.

Mr. Putin certified in public that the man in the video, widely believed to have been arranged and then filmed by the F.S.B., was indeed the prosecutor general. Mr. Skuratov resigned, the corruption investigation ended and a grateful Mr. Yeltsin named Mr. Putin prime minister, clearing his path to the presidency.

Unlike entirely fabricated reports of criminal or simply embarrassing behavior, kompromat is generally true, though photographs and videos are sometimes tinkered with to heighten the embarrassment. This makes it a particularly blunt and dangerous weapon that can easily backfire.