A massive cyberattack on the Marriott hotel chain was part of a Chinese intelligence-gathering effort, The New York Times reported on Tuesday, citing two people briefed on the preliminary results of the investigation.

The hackers are suspected of working on behalf of the Ministry of State Security, The Times added.

An unknown attacker stole information including emails, names, addresses, passport numbers and possibly payment card information, in a slow-moving attack that lasted four years. The breach, which affected 500 million guests, was disclosed by the chain in late November, two months after it was discovered.

The Justice Department is preparing to announce new indictments — possibly within days — against Chinese hackers working for the intelligence and military services, according to the NYT, which cited government officials speaking on condition of anonymity.