China has denied involvement in the Office of Personnel Management (OPM) hack that compromised over 14 million US government workers' details.
Foreign ministry spokesperson Lu Kang denied during a press conference US accusations that the attack was mounted by state-sponsored Chinese hackers.
"In response to what Senator Harry Reid said, I want to point out that what the international community has heard and seen the most over recent years are revelations about the engagement of the US in a large amount of illegal cyber activities," he said.
"Relevant people from the US should not forget that the US still owes the international community an explanation on issues concerning cyber attack and theft. It is impossible to muddle through by diverting people's attention.
"Maybe it is better to clarify one's own matters before rushing to make unfounded accusations against others, so as to make oneself sound more convincing."
Lu's comments refer to ongoing questions about the US PRISM mass surveillence campaign.
The White House revealed earlier in June that OPM systems had been hit with a major cyber assault affecting as many as 14 million staff.
The intrusion that led to the loss occurred in April this year, and the OPM has already pulled in the FBI and the US Department of Homeland Security's Computer Emergency Readiness Team (US-CERT) to investigate the incident.
The OPM has promised to advise the affected four million of the issue and to offer advice on not falling foul of any resulting exploit efforts. It is also recommending that victims get a credit report and keep an eye on their identity.
Other advice, such as a recommendation that individuals do not open suspicious mail from unknown parties, is also provided.
"Protecting our Federal employee data from malicious cyber incidents is of the highest priority at OPM," said OPM director Katherine Archuleta.
"We take very seriously our responsibility to secure the information stored in our systems, and in coordination with our agency partners, our experienced team is constantly identifying opportunities to further protect the data with which we are entrusted."
Politicans have criticised the government department for the latest data loss incident.
The last few months have seen a series of massive data breaches that have affected millions of Americans. #DataBreach— Adam Schiff (@RepAdamSchiff) June 4, 2015
The latest breach, which has exposed personal information of more than 4 million current & former federal employees is among most shocking.— Adam Schiff (@RepAdamSchiff) June 4, 2015
Security experts believe the attack came from China and is another sign of that country's habit of hacking the US.
"[This is] yet another indication of a foreign power probing successfully and focusing on what appears to be data that would identify people with security clearances," said Susan Collins, a member of the Senate Intelligence Committee.
Adam Schiff, a member of the of the House intelligence committee, suggested that enough is enough and that the US desperately needs to improve its security provisions and protection.
"It's clear a substantial improvement in our cyber databases and defenses is perilously overdue," he tweeted.
The FBI has also confirmed it is looking into the details of the breach. "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.”
Grayson Milbourne, security intelligence director at Webroot, said that while details were still coming to light, it was clear the nature of the attack meant it was a nation-state backed incident.
“Until we can understand what level of data access was achieved, we won’t know the full impact. But, based on the characteristics of the attack, it’s likely the perpetrator was a nation-state," he said.
"Clearly, the government’s approach to cybersecurity needs to be reformed, prioritised and accelerated. That the breach might have been carried out by the Chinese does not absolve the OPM of blame.
"The issue here is the government’s technological failings and what it should be doing to prevent future attacks.”
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