The hackers are accused of stealing the sensitive personal information on some 145 million Americans, in one of the world's largest ever data breaches, said Attorney General Bill Barr.

"This was a deliberate and sweeping intrusion into the private information of the American people," he said.

The Justice Department indictment charged four members of the Chinese army's 54th Research Institute -- Wu Zhiyong, Wang Qian, Xu Ke and Liu Lei -- with multiple counts of hacking, computer fraud, economic espionage and wire fraud.

Officials said it took well over a year to track them through the 34 servers in 20 countries they allegedly used to hide their tracks.

"This was an organized and remarkably brazen criminal heist of sensitive information of nearly half of all Americans, as well as the hard work and intellectual property of an American company, by a unit of the Chinese military," Barr said.

The hack stunned US officials, and came in the wake of a similar hack on the US government's civil service database, also blamed on the Chinese.

US officials believe the Chinese military has undertaken the hacks to amass a huge amount of data on Americans for strictly intelligence purposes.

FBI Deputy Director David Bowdich said there was no evidence yet of the Equifax data having been used, for example to hijack a person's bank account or credit card.

But he added: "If you get the personal identifying information of people, you can do a lot with that."