The White House has refused to confirm rumours that Russians were behind a cyberattack against it, contradicting reports from the US broadcaster CNN.
The office of the US president insisted that its systems were not compromised in the attack, which took place last October, in one of the most serious cyberattacks on the US government on public record.
Ben Rhodes, deputy national security advisor, said: "There was an event last year, we have classified systems that are secure. We don’t talk about where cyber intrusions originate from."
CNN claims that the attack, which targeted an unclassified White House network, resulted in hackers obtaining details of US president Barack Obama’s schedule, citing US officials as the source.
Investigators also believe that the White House was accessed via the State Department responsible for foreign affairs, according to the broadcaster, with one official claiming the intrusion is ongoing.
It is also alleged the attack began with a spear phishing campaign, a basic form of hacking in which victims are sent misleading emails designed to steal login data.
Jeremiah Grossman, interim chief executive of WhiteHat Security, said: "If the White House or the State Department can’t keep our foreign hackers with the infinite resources at their disposal, what chance does the average company have? Not to mention the everyday person.
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"Secondly, whatever new legislation the White House or Congress is planning, does it have any chance of preventing this kind of incident from happening again?"
Tensions among world powers over cybersecurity have grown steadily over the last few years, with the US recently accusing North Korea of involvement in the devastating hack on Sony in November.
The US has long maintained that China sponsors hacking groups to target American corporations in a bid to steal sensitive data and intellectual property.
Whilst similar accusations have not often been levelled against Russia, the country is known for harbouring gangs of cybercriminals which often run campaigns against Western citizens.
