US Democratic presidential hopeful Hillary Clinton has accused China of stealing commercial secrets and government information.
She accused China of “trying to hack into everything that doesn’t move in America”، and urged vigilance.
US officials had named China as the chief suspect in the massive hack of the records of a US government agency earlier this year.
China had denied any involvement، and called US claims “irresponsible”.
The hack against the OPM is not the first time that China has been blamed for a cyber attack against the US.
An earlier attempt to breach OPM networks was blocked in March 2014، with the US saying China was behind the attack.