Community Health Systems, the US hospital operator, said that Chinese hackers have stolen private information about 4.5m of its patients, the largest number of accounts compromised in such an attack, adding to long-running tensions between the two nations over cyber crime.
In a filing to the US Securities and Exchange Commission on Monday, the company said it believed its computer network was hacked in April and June this year.
It said that forensic experts believe the attack was carried out by a China-based group using advanced malware and technology, though it did not specify the name of the organisation it believes is responsible for the hack.