The US government has reportedly “penetrated” Russia’s telecommunications networks and electric grid to be ready to “hit back” in case Russian intelligence agencies carry out a cyberattack on election day.

An anonymous senior intelligence official told NBC news that the US would only deploy its own cyber attack “if necessary”.

It has been an open secret for years that the US has infiltrated critical online infrastructure of other nations like Russia and China, while the US has accused them of doing the same.

Days before the 2016 presidential election, US officials are concerned that adversaries could cause mayhem on Tuesday by releasing fake documents, creating bogus social media profiles to spread misinformation online such as rigged counting and tampering with state voting registration systems.

The news comes the same day that the hacker “Guccifer 2.0” - a front for Russian intelligence - tweeted that it would monitor the US elections “from inside the system”.

The Department of Homeland Security briefed reporters on Friday that they were “very concerned” about confusion on election day, but were confident that no breach would influence the result of the election.

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Representative Adam Schiff of the House Select Committee on Intelligence told CNN: “They are capable of doing damage, they are capable of sowing further disarray.

“Will they end up doing it? We don't know, and I think we are taking all the precautions that we can.”

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The DHS has offered “cyberhygiene scans” to all 50 states, but not all of them have accepted the help. The government has also readied “incident response teams” to be deployed wherever there might be a cybersecurity incident on Tuesday.

A spokesman from the US Secret Service told The Independent: "The Secret Service does not disclose information related to our means and methods of protective operations."

Voter registration system databases in Illinois and Arizona were tampered with earlier this year. The US government has also officially accused Russia of hacking the emails of the Democratic National Committee in June.

Two senior officials from the DNC told Mother Jones that a security sweep in late October found evidence - a radio signal near the chairman’s office - to suggest that their headquarters in Washington DC had been “bugged”, and they had submitted evidence to the FBI. No devices or culprits have been found.

The alert that foreign adversaries were hacking the US to gain information and potential control of everything from chemical facilities to water treatment plants was first brought up to US congress in 2014 by National Security Agency chief Mike Rogers.

The US has been laying its own military cyber ground for years. NBC reported that the US penetrated Iraqi networks during the Iraq invasion of 2003, urging generals to surrender and temporarily cutting electricity in Baghdad.

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The US also reportedly worked with Israel in 2009 and 2010 to deploy a cyber weapon to destroy Iranian nuclear centrifuges.