A year before the Boston Tea Party, Benjamin Franklin was at the center of a high-profile leak that fueled anti-British sentiment in the Massachusetts Colony.

In 1772, Franklin was living in London as the representative of several American colonies, including Massachusetts. He saw his role as maintaining peaceful and productive relations between the colonies, Parliament and the Crown. When the Stamp Act of 1765 caused an uproar in the colonies, for example, Franklin’s testimony before Parliament helped get the unpopular act repealed.

Franklin was also the Postmaster General of the Parliamentary Post in America, a position he had held since 1753. In December 1772, Franklin received a strange package from an anonymous sender. The package contained 13 letters written between Massachusetts Governor Thomas Hutchinson, Lieutenant Governor Andrew Oliver and British military officials.

In the letters, the colonial overlords of Massachusetts complained to British authorities about unrest in the colony over English taxation. Instead of taking the people’s side, Hutchinson and Oliver recommended that Parliament send more English troops to Massachusetts and impose even more restrictive measures to keep the Americans in line.

Recognizing the explosive nature of the letters, Franklin sent copies to Samuel Adams in Boston with a request to keep the contents secret until appropriate action could be taken. Adams ignored Franklin’s request and published the letters in the Boston Gazette in June 1773. Angry Bostonians called for the immediate removal of Hutchinson and Oliver.

Back in London, Parliament launched an investigation into the leaked letters. When two men were wrongly accused (and wounded each other in a botched duel), Franklin publicly admitted his role in the affair.

Franklin wrote a letter to the London Chronicle defending his actions with trademark wit. Franklin said that he plainly understood the letter writers’ fear that they would fall into American hands. “That apprehension was, it seems, well founded; for the first [Colony Agent] who laid his hands on them thought it his duty to transmit them to his Constituents.”

For his breach of trust, Franklin was dismissed as Postmaster General but continued to try to salvage relations with the British until 1775, when he returned home to join the Second Continental Congress.

In 1916, Woodrow Wilson was re-elected president of the United States largely on his promise to keep America out of the war raging in Europe. But on February 24, 1917, British intelligence leaked the contents of a secret German telegram that helped convince a reluctant Wilson and Congress to enter World War I.

As early as 1914, British codebreakers attempted to crack German military communications, especially those related to submarine warfare. There was a major breakthrough in October 1914 when the Russian military recovered a German naval codebook on a drowned German sailor. By 1917, British intelligence was actively eavesdropping on most German military and diplomatic communications.

In January of 1917, British intelligence got its hands on a coded telegram sent from German Foreign Minister Arthur Zimmermann to the German ambassador in Mexico. The contents were nothing short of a bombshell. The telegram revealed that the Germans planned to resume unrestricted submarine warfare in February, which went against an existing pact. Knowing this controversial move would likely bring the United States into the war, Germany proposed a secret alliance with Mexico.

“[W]e make Mexico a proposal or alliance on the following basis,” wrote Zimmermann, “make war together, make peace together, generous financial support and an understanding on our part that Mexico is to reconquer the lost territory in Texas, New Mexico and Arizona.”

Although decoded in January, Britain held onto the explosive telegram until late February, by which time the U.S. had already severed diplomatic ties with Germany over its unrestricted submarine attacks. The British timed the leak to have maximum effect on U.S. foreign policy and public opinion about the war. The “Zimmermann Telegram” was published in American newspapers on March 1, 1917, and the leaked document had precisely the intended effect—Congress declared war on Germany a month later.

Interestingly, the World War I era was also when Congress passed the Espionage Act of 1917, explicitly making it a crime to “willfully cause or attempt to cause insubordination, disloyalty, mutiny, [or] refusal of duty” in the military. The Espionage Act was largely intended to clamp down on antiwar dissent, but decades later it would be used to prosecute leakers.

“Even though the Espionage Act was developed in the World War I era and for a very different purpose, it essentially became the mechanism to help prosecute the mishandling of information after World War II,” says Mistry. “If anybody is found giving information to those who shouldn't have it, they can be charged under the Espionage Act.”

After World War II, the U.S. military intelligence regime expanded into a larger Cold War intelligence apparatus that included the CIA and NSA. With the creation of those entities, there was an exponential increase in the amount of classified material.

“The government needed to protect all of this information they were collecting,” says Jamil N. Jaffer, assistant professor of law at George Mason University Scalia Law School, “and that included the sources and methods of collection.”

During the Vietnam War, intelligence analyst Daniel Ellsberg worked on a study commissioned by Defense Secretary Robert McNamara about the wisdom of the war. Ellsberg was part of a team that investigated America’s military involvement in Southeast Asia dating back more than two decades.

The product was a 7,000-page classified report titled, “History of U.S. Decision-Making in Vietnam, 1945–68.” In Ellsberg’s eyes, the report proved that American presidents and military leaders had willfully misled the public about America’s role in Vietnam. Ellsberg suffered a crisis of conscience and decided that the world needed to know the truth about the war.

In March 1971, Ellsberg delivered copies of “The Pentagon Papers” (as they became known) first to the New York Times and then the Washington Post. After long deliberations about the ethics and legality of publishing classified information, both papers went public with the first sections of the report. The Nixon administration immediately sued to halt further publication.

The case was so important that the Supreme Court came back from recess to hand down a 6-3 decision against the Nixon administration. The publication of “The Pentagon Papers” could proceed, but nothing in the Court’s decision guaranteed that future leaks would be covered by the First Amendment.

In a separate trial, Ellsberg was charged with violating the Espionage Act. But before a verdict was reached, it was revealed that the Nixon White House had sent “plumbers” to break into Ellsberg’s psychiatrist’s office in order to discredit him. Ellsberg’s espionage case was thrown out and the controversy over “The Pentagon Papers” was quickly eclipsed by the unfolding Watergate scandal.

Ellsberg had believed that by leaking “The Pentagon Papers” he could end the Vietnam War, or at least sway public opinion squarely against it. But the report wasn’t the smoking gun that he’d hoped it would be.

“By that point in the war, the country's views were largely fixed on both sides,” says Jaffer, founder and executive director, National Security Institute, GMU Scalia Law School. “So the Pentagon Papers didn’t fundamentally change the dynamic. Ironically, the government’s attempt to keep the report out of the public eye by taking it to the Supreme Court actually may have raised its profile.”

The controversial website WikiLeaks was launched in 2006 by Julian Assange, an Australian-born computer programmer. The mission of WikiLeaks was to offer a public clearinghouse for classified or otherwise secret government and corporate documents. WikiLeaks first gained international prominence in 2010, when it published what is still the largest classified leak in history.

Chelsea Manning (then known as Bradley Manning) was working as a U.S. Army intelligence officer in Baghdad when she uncovered some disturbing classified records. The documents suggested that the U.S. military had covered up the deaths of 15,000 civilians in Afghanistan and Iraq. She also found 2007 video footage of a U.S. Apache helicopter shooting enemy targets that turned out to be Iraqi civilians and two Reuters journalists.

Following in the footsteps of Ellsberg, Manning tried to share the documents with newspapers like the New York Times and the Washington Post, but they didn’t respond, reports Wired. So Manning reached out to Assange, who helped the American whistleblower upload more than 700,000 classified military and diplomatic records to WikiLeaks.

Jaffer says that Assange and WikiLeaks represented an entirely new type of threat to U.S. national security interests.

“This wasn't some random do-gooder from the United States who wanted to identify government fraud and abuse, or protect Americans’ privacy and civil liberties,” says Jaffer. “This was a foreign national running a website whose entire purpose is to undermine the foreign policy and national security interests of the United States.”

Unlike Ellsberg, Manning was ultimately convicted of violating the Espionage Act and sentenced to 35 years in prison by a military court-martial. President Obama later commuted her sentence to seven years.

Edward Snowden’s revelations about an unconstitutional mass surveillance program was a black eye for the U.S. Intelligence Community, but not everyone considers Snowden a “hero.”

From 2006 to 2012, Snowden worked as a contractor with the CIA and the NSA as a computer systems administrator. This work gave him a front-row seat to the intelligence agencies’ highly classified anti-terrorism programs. Snowden was shocked to learn that the George W. Bush administration and Congress had authorized the NSA to collect phone and email data from American citizens without a specified warrant, which was unconstitutional.

Snowden decided to take this information public, but he saw what happened to Chelsea Manning when she uploaded classified files to WikiLeaks. Instead, Snowden reached out to newspaper reporters over secure channels and arranged to meet them in Hong Kong to hand over the files.

On June 5, 2013, The Guardian newspaper in the UK published the first article exposing the NSA’s mass surveillance programs as well as other covert NSA activities worldwide, including bugging the cellphones of foreign leaders. The embarrassing revelations led to U.S. congressional hearings and significant changes to NSA surveillance tactics. The shockwaves also reverberated around the globe.

“Snowden triggered discussions all over the world in terms of the scale of America’s ability to surveille citizens around the world and what local governments were doing to either push back or to help facilitate it,” says Mistry.

For his part, Jaffer doesn’t think that Snowden should be hailed as a “whistleblower,” because much of what he leaked compromised legal intelligence-gathering efforts worldwide. Also, Jaffer says, the U.S. intelligence community has internal channels for reporting concerns related to classified programs.

“Edward Snowden had a million other ways to call attention to this program,” says Jaffer. “He could have gone to the inspector general of his agency or of the Intelligence Community. He could have gone to the House or Senate Intelligence Committee. He could have gone to a lot of people to raise his concerns. He didn't do any of that. Instead, he flew across the globe, released tons of highly classified documents having nothing to do with the rights of Americans, and fled to Russia, where he now lives as a Russian citizen under the protection of Vladimir Putin.”

Snowden is wanted in the United States for charges of violating the Espionage Act.