Famous whistleblowers

Ellsberg was A U.S. military analyst who, while employed by the RAND Corporation in 1971, released the Pentagon Papers, a top-secret Pentagon study of U.S. government decision-making in relation to the Vietnam War, to The New York Times.

W. Mark Felt

A 2005 Vanity Fair article exposed Felt, a former FBI official, as "Deep Throat": The long-anonymous source who leaked secrets about President Nixon's Watergate cover-up to The Washington Post in the early 1970's.

Ultimately, Felt's devastating leaks as The Washington Post's secret Watergate source helped undermine Nixon's presidency.

Read more: W. Mark Felt, "Deep Throat," Dies At 95

Bradley Manning

Pfc. Bradley Manning went on trial this month over the biggest leak of classified material in American history. Manning admitted turning over hundreds of thousands of documents to the anti-secrecy website WikiLeaks, pleading guilty earlier this year to charges that could bring 20 years behind bars. But the military pressed ahead with a court-martial on more serious charges, including aiding the enemy, which carries a potential life sentence.

Read more: Bradley Manning dumped info into enemy hands, prosecutor says

Sherron Watkins

Sherron Watkins, an Enron Corporation Vice-President, exposed one of the largest accounting frauds in history, leading to a 24-year prison sentence for CEO Jeff Skilling.

Watch:Eye To Eye: Former Enron VP

Frank Serpico

The former New York City police detective helped expose widespread corruption and bribery within the NYPD in the early 1970s.

Coleen Rowley

A Minneapolis-based FBI agent, Rowley accused FBI headquarters of hindering efforts to investigate a suspected terrorist before September 11.

Linda Tripp

While working at the Pentagon's public affairs office, Linda Tripp befriended Monica Lewinsky and later, secretly recorded their phone conversations. The tapes became a centerpiece of the investigation that exposed Lewinsky's affair with then-President Bill Clinton.

Dr. Jeffrey S. Wigand

Formerly a research scientist for Brown & Williamson, Wigand was the first major tobacco insider to reveal that cigarette companies were consciously trying to get us hooked on nicotine, despite tobacco executives' public statements to the contrary. A two-part "60 Minutes" story that aired in 1996 inspired a Hollywood film, "The Insider," starring Russell Crowe.

Watch more:Wigand: 60 Minutes' Most Famous Whistleblower