File picture, showing a four-rotor Enigma machine, right, once used by the crews of German U-boats in World War II to send coded messages, which British World War II code-breaker mathematician Alan Turing, was instrumental in breaking, and which is widely thought to have been a turning point in the war.
ALEX DORGAN-ROSS, ASSOCIATED PRESS
In this October 1967 file photo President Lyndon B. Johnson talks to troops at Cam Ranh Bay, South Vietnam, during the Vietnam War. Forty years after the leak of the Pentagon Papers, the secret government study chronicling deception and misadventure in U.S. conduct of the Vietnam War, the report is being released in full Monday, June 13, 2011, by the National Archives and presidential libraries. It was leaked primarily by foreign policy analyst Daniel Ellsberg, becoming one of the most dramatic episodes of whistle-blowing in U.S. history. At right is Gen. William Westmoreland.
In this June 30, 1971 file picture, workers in the New York Times composing room in New York look at a proof sheet of a page containing the secret Pentagon report on Vietnam.
Marty Lederhandler, Associated Press
In this Saturday, April 1, 1972 file picture, Daniel Ellsberg, chief defendant in the Pentagon Papers case, addresses a crowd at the State Capitol in Harrisburg, Pa. following an anti-war parade that ended at the Capitol. The rally was also held in support of the seven defendants in the Harrisburg conspiracy trial.
Rusty Kennedy, Associated Press
In this Nov. 25, 1972, file photo President Nixon confers with his adviser Henry Kissinger, right, after Kissinger's return from a week of secret negotiations in Paris with North Vietnam's Le Duc Tho. Ellsberg served with the Marines in Vietnam and came back disillusioned. He was a protege of Kissinger's, who called the young man his most brilliant student.
File, Associated Press
Former President Richard Nixon waves Oct. 29, 1980, as he leaves the U.S. District Court in Washington after testifying on behalf of high FBI officials W. Mark Felt and Edward Miller, that the FBI had direct authority from the president to conduct warrantless break-ins in foreign intelligence cases important to national security. It was Felt, the FBI second-in-command, alias "Deep Throat", who leaked crucial information about Nixon administration corruption that led to the unraveling of the presidency.
Charlie Tasnadi, Associated Press
In this June 25, 2012 file photo, Army Pfc. Bradley Manning, right, is escorted out of a courthouse in Fort Meade, Md. The Army private charged in the largest leak of classified material in U.S. history says he sent the material to WikiLeaks to enlighten the public about American foreign and military policy on Thursday, Feb. 28, 2013.
Patrick Semansky, File, Associated Press
Julian Assange, founder of WikiLeaks speaks at a press conference in London, Monday, Feb. 27, 2012.
Kirsty Wigglesworth, Associated Press
Last Friday it was revealed in the Washington Post that the Chinese hacked into crucial U.S. military networks, gaining access to dozens of weapons systems. "This is billions of dollars of combat advantage for China. They've just saved themselves 25 years of research and development. It's nuts," a senior official told the Post.
While certainly troubling, it isn't the first time the U.S. goverment has found itself with a major intelligence leak or security breach. From the Mexican-American war to WikiLeaks, the U.S. has long been dealing with headline-grabbing intelligence leaks. "
Here is a list of 15 of the most infamous security leaks/breaches in history.