REPORTS that Chinese hackers were behind a massive cyber attack on US federal employees’ personal data were yesterday condemned by Beijing as “irresponsible.”

On Thursday, the US government said hackers accessed the personal data of at least 4 million current and former federal employees. Officials told reporters that China was suspected.

“Cyber attacks are generally anonymous and conducted across borders and their origins are hard to trace,” foreign ministry spokesman Hong Lei said at a regular briefing.

As a result of the incident uncovered in April, the US Office of Personnel Management said it “will send notifications to approximately 4 million individuals.” It added that additional exposures “may come to light.”

The government’s personnel department handles hundreds of thousands of sensitive security clearances and background investigations on prospective employees each year.

It was not immediately clear whether the hack affected President Barack Obama, other senior government officials or the intelligence community.

The Washington Post and other US media cited government officials as saying that Chinese hackers were behind the breach.

“We have seen a lot of media reports and opinions like this recently,” Hong said.

The Chinese embassy in Washington countered that such attacks would not be allowed under Chinese law.

“Chinese laws prohibit cyber crimes of all forms. China has made great efforts to combat cyber attacks in accordance with Chinese laws and regulations,” embassy spokesman Zhu Haiquan said.

The FBI and Department of Homeland Security are said to be investigating the attack. The FBI in a statement said it “will continue to investigate and hold accountable those who pose a threat in cyberspace.”

The US government said it will, through a third party, offer US$1 million in identity theft protection services at no cost.

Tougher security

“Protecting our federal employee data from malicious cyber incidents is of the highest priority,” Katherine Archuleta, director of the personnel management office, said.

Her agency said the intrusion may have begun late last year and predated the adoption of tougher security controls.

The new measures include restricting remote access, screening business connections and deploying anti-malware software.

The incident is the latest in a series of major breaches that have shown the vulnerability of the federal government.

Last year, Russian hackers are believed to have accessed unclassified computer systems at the White House and the State Department.

Last month, hackers stole information on 100,000 taxpayers from online computers of the US Internal Revenue Service.

The United States has struck an increasingly tough tone about cyber attacks in recent months.

Admiral Michael Rogers, who heads the National Security Agency and US Cyber Command, has said that future attacks could prompt a response with conventional weapons.

In February, US Director of National Intelligence James Clapper said that it was a steady stream of low-level cyber attacks that posed the most likely danger to the US, rather than a potential digital “Armageddon.”