Marriott hack blamed on China

That massive data breach that hit hotel group Marriott? Now there are clues the hackers behind it were working for a Chinese government intelligence gathering operation.

Let's refresh on how bad the hack disclosed just last week ago really was.

500 million people were affected.

Unauthorized access to the Starwood network since 2014 " For approximately 327M of these guests, the info includes some combination of name, mailing address, phone number, email address, passport number.

Today, sources familiar with the breach detailed what they know to Reuters:

Marriott said last week that a hack that began four years ago had exposed the records of up to 500 million customers in its Starwood hotels reservation system.

Private investigators looking into the breach have found hacking tools, techniques and procedures previously used in attacks attributed to Chinese hackers, said three sources who were not authorized to discuss the company's private probe into the attack.

That suggests that Chinese hackers may have been behind a campaign designed to collect information for use in Beijing's espionage efforts and not for financial gain, two of the sources said.

While China has emerged as the lead suspect in the case, the sources cautioned it was possible somebody else was behind the hack because other parties had access to the same hacking tools, some of which have previously been posted online.

Identifying the culprit is further complicated by the fact that investigators suspect multiple hacking groups may have simultaneously been inside Starwood's computer networks since 2014, said one of the sources.

"The Chinese Embassy in Washington did not return requests for comment."