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.
I used to have opinions about whether these attributions are true or not. These days, I tend to wait and see.