Cyber security
China denies involvement in massive US data breachPawel Kopczynski/Reuters file photoReuters

China has denied any hand in the massive data breach in the US which has affected nearly four million people.

A spokesperson for the Chinese embassy in Washington said in a statement: "Cyber-attacks conducted across countries are hard to track and therefore the source of attacks is difficult to identify. Jumping to conclusions and making hypothetical accusation is not responsible and counterproductive."

Zhu Haiquan added: "Cyberattack is a global threat which could only be addressed by international cooperation based on mutual trust and mutual respect."

US officials earlier alleged that a massive data breach - described as the biggest ever - of government networks, had been carried out compromising information of up to four million former and current federal employees.

The Office of Personnel Management (OPM), which runs background checks of employees, said it had detected the malicious activities suspected to be sourced from Chinese systems, in April this year. The Department of Homeland Security later confirmed it to be a cyber-attack and warned that personal information of the staff could have been affected.

Subsequent to the incident, the OPM said it had alerted the susceptible people, whose data may have been stolen, and emphasised additional precautions have been put in place.

The cyber-attack could have hit nearly every federal government agency in the US. As the investigation continues, reports suggest millions of others could also have been affected by the attack.

Multiple US officials, who mostly spoke on condition of anonymity, have either directly or indirectly pointed fingers at China for the attack.

The FBI has launched a probe into the matter promising the hackers who are behind the attack would be held accountable.

"The FBI is working with our interagency partners to investigate this matter. We take all potential threats to public and private sector systems seriously, and will continue to investigate and hold accountable those who pose a threat in cyberspace," the bureau said.