Chinese spies have had access to the private emails of top Obama administration officials for several years, NBC News reported on Monday, citing top secret documents and a senior U.S. intelligence official.

Documents from a 2014 National Security Agency (NSA) briefing revealed that the intrusion was reportedly ongoing at the time. The intrusion was first detected in April 2010.

The U.S. intelligence official, who was not identified, said the email accounts assigned by the government were not compromised. According to NBC News, the names of the officials affected by the act of cyber-espionage have not been revealed. Hillary Clinton, a 2016 presidential candidate, was using a private email account at the time of the attack, which coincided with her tenure as secretary of state in the Obama administration.

“All top national security and trade officials” were targeted, the official said.

“All top national security and trade officials” were targeted, the official said. The U.S. reportedly called the attack “Dancing Panda” and later “Legion Amethyst.”

The contacts of the compromised email accounts may have been targeted as well, reported NBC News, according to a top-secret document. The Chinese hackers allegedly harvested the contacts and sent them malware in an attempt to “[exploit their] social networks.”

The report notes that a document previously leaked by U.S. whistleblower Edward Snowden revealed that, in 2010, China had attempted to spy on four U.S. officials by injecting spyware into their computers.

In 2013, NBC News first reported that the U.S. intelligence had traced cyberattacks targeting 2008 presidential nominees Barack Obama and John McCain to “hacking units backed by the People’s Republic of China.”

Earlier this year, the Office of Personnel Management (OPM) suffered one of the most devastating cyberattacks in U.S. government history. The White House has so far refrained from officially blaming China for the OPM hack. A senior administration official reportedly told the New York Times that President Obama is searching for a way to retaliate against the Chinese without further escalating the cyberconflict.

H/T NBC News | Illustration by Max Fleishman