The FBI is working to determine who is responsible

America confirms targeting its government networks with a "major" cyber attack

O'Brien cut short a European visit and returned to Washington to deal with the attack.

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The US government confirmed yesterday that a recent hacking campaign had infected its networks, and said it was "large and continuous."

Informed sources told «Reuters» this week that hackers, believed to be working for Russia, spied on the internal emails of the US Treasury and Commerce Department, and that there are fears that the infiltration discovered so far is only the tip of the iceberg.

"This is an evolving situation, and while we continue to work to fully understand the scope of the campaign, we know that this breach affected networks within the federal government," said a joint statement issued by the FBI, the Agency for Cybersecurity and Infrastructure Security, and the Office of the Director of National Intelligence.

"Over the past few days, the FBI, the Cybersecurity and Infrastructure Security Agency and the Office of the Director of National Intelligence have become aware of a large and ongoing cybersecurity campaign," the statement added.

He also said, "The FBI is investigating and gathering information in order to identify, prosecute and disable those responsible for the threat."

The White House National Security Adviser Robert O'Brien cut short a European visit on Tuesday and returned to Washington to deal with the attack.

"Politico" newspaper quoted a US administration official as saying that O'Brien's return came to coordinate the government's response to the attack on the Treasury, Trade and Homeland Security ministries.

The breach affected networks within the government.

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