The hacking attack on Anthem, the second-largest health insurer in the US, is suspected to be sponsored by the Chinese state, according to media reports.
Bloomberg, citing three people familiar with the US probe into the case, reported that available evidence points to Chinese state-sponsored hackers who are stealing personal information from health-care companies for purposes other than pure profit.
Reuters separately reported that the US states investigating the cyberattack are examining its possible ties to China. The Wall Street Journal citing people close to the investigation reported that some tools and techniques used against Anthem were similar to ones used in previous attacks linked to China.
The hack, which is one of the biggest thefts of medical-related customer data in the history of the US, is expected to have exposed social security numbers and other sensitive information of some 80 million people.
A US government official told Bloomberg, the attack appears to have targeted the personal lives and computers of a select group, including defence contractors, government workers and others.
Two people familiar with the investigation said China is the early suspect, as the attack left "fingerprints" of a nation-state.
Anthem earlier said attackers had gained unauthorised access to its IT system and obtained personal information of its current and former members. There is no evidence that credit card or medical information were compromised, according to the company.
Anthem noted it contacted the FBI and has been fully cooperating with the investigation. It also retained cybersecurity firm Mandiant to evaluate its systems and identify solutions.
Cybersecurity has recently become a major concern for large companies, governments and individuals in line with the rising number of hacking attacks and the leakage of large amounts of data.
Big US companies including Target Corp, Home Depot Inc, JPMorgan Chase & Co and Sony Pictures have been victims of sophisticated hacking attacks, exposing the private data of hundreds of millions of Americans.
Earlier, the US indicted five Chinese military officials who hacked the websites of US companies for the benefit of Chinese rival companies, souring relations between the economic powerhouses. China has denied the accusations, and said it doesn't conduct espionage through hacking.