Earlier this week, federal investigators revealed that the internal networks of the US government's Office of Personnel Management, which manages employee records for every federal agency, had been compromised by hackers. Now new information obtained by Reuters suggests the compromised data spans three decades, prompting the news agency to call the hack "one of the largest known cyberattacks on federal networks."

"This is deep. The data goes back to 1985," a US official told Reuters. "This means that [the hackers] potentially have information about retirees, and they could know what they did after leaving government."

"This is deep."

The hack, which reportedly affected around 2 million workers, exposed personal, but not highly classified data, such as birthdates, addresses, Social Security numbers, and bank information. Officials say access to the data may prove useful in testing passwords to sensitive government sites, according to Reuters.

The hackers are believed to be based in China, but US officials have not definitively linked the attack to the Chinese government. OPM also knows what types of data were taken, but not the exact data, according to a US House of Representatives memo seen by Reuters.

A similar data breach affected the OPM earlier this year, but no personal information was compromised.