Chinese calls US hacking suspicions 'irresponsible' begs for more trust
Chinese hackers are suspected of carrying out a "massive breach" of the personal data of nearly four million United States government workers.
The Office of Personnel Management (OPM) confirmed that both current and past employees had been affected.
Officials say the breach could potentially affect every federal agency.
US officials said the hackers were believed to be based in China.
However, Beijing responded by calling such claims "irresponsible".
OPM said it became aware of the breach in April during an "aggressive effort" to update its cyber security systems.
It said it would be contacting all those individuals whose personal data may have been breached in the coming weeks, and offering them 18 months of free credit monitoring and identity theft insurance.