A major security breach from the Pentagon leading to the disclosure of military documents has shone the spotlight on how the US looks after its secrets.

A 21-year-old has been arrested in the latest investigation.

But the new revelations are far from the first high-profile classified leaks to embarrass the US.

Here are some of the other cases that have hit the headlines in recent years.

Chelsea Manning

The former US Army intelligence analyst was behind the largest known unauthorised release of sensitive US government material.

Manning was convicted of espionage and other offences by court martial in 2013.

She leaked nearly 750,000 documents, videos, diplomatic cables and battlefield accounts to the whistleblowing platform WikiLeaks while she was serving in Iraq in 2010.

Sentenced to 35 years in jail, she was released in 2017 after former US president Barack Obama commuted her sentence.

Previously known as Private Bradley Manning, the former soldier now identifies as a woman and underwent gender transition while in jail.

Among the documents she released were millions of diplomatic cables and a 2007 video of a US helicopter in Baghdad firing on a group of civilians.

The attack killed a dozen people, including two Reuters photographers, and wounded two children.

In response, the then Obama administration introduced the Insider Threat Program, which required US agencies to upgrade safeguards against unauthorised disclosures.

Its security measures included routinely monitoring and auditing classified computer networks “to detect, monitor, and analyse anomalous user behaviour for indicators of misuse”.

Manning was jailed again in 2019 for contempt of court after refusing to give evidence to a grand jury investigation into WikiLeaks.

Julian Assange

The WikiLeaks founder is currently being held at the high-security Belmarsh Prison in southeast London while he continues a lengthy legal fight to avoid extradition to the US.

He was arrested in London in 2019 after spending seven years holed up in the city’s Ecuadorian Embassy.

Assange is wanted by the US for an alleged conspiracy to obtain and disclose national defence information after WikiLeaks published hundreds of thousands of leaked documents relating to the Afghanistan and Iraq wars.

If convicted of breaching the Espionage Act, Assange faces up to 175 years in jail.

Read more on new Pentagon leaks:
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What do the highly classified documents say?
How did someone so young have access?

He has always denied any wrongdoing and attracted support for his case from human rights groups, parliamentarians and celebrities, including the late fashion designer Vivienne Westwood.

Assange spent seven years in Ecuador’s London embassy to avoid extradition to Sweden to face allegations of rape and sexual assault.

He was dragged out of the building after Ecuador revoked his asylum status.

Assange and his wife Stella, a lawyer, married at Belmarsh in March last year and have two children together.

Edward Snowden

The former US intelligence contractor fled to Russia after leaking secret files in 2013 that revealed vast domestic and international surveillance operations carried out by the National Security Agency (NSA), where he worked.

Washington has sought his return for years to face trial on espionage charges.

Russia granted Snowden permanent residency rights in 2020, paving the way for him to obtain Russian citizenship, which he received last September.

He has subsequently sworn an oath of allegiance to his adopted country and received a Russian passport, his lawyer told the state news agency TASS.

A US appeals court has previously found the spying activities Snowden had exposed were unlawful and that the US intelligence leaders who publicly defended it were not telling the truth.

Snowden, who has kept a low profile in Russia but occasionally criticised the Kremlin on social media, said in 2019 he was willing to return to the US if he was guaranteed a fair trial.