President Barack Obama declared the threat of cyber attacks by foreign agents a 'national emergency' as he unveiled plans to impose sanctions on hackers in the wake of an epidemic of attacks against American networks. Obama took aim at Russia, China and Iran as he revealed an executive order which will allow the U.S. Treasury  to freeze or block assets of those involved in attacks on 'critical' American computer networks. The announcement followed a series of high profile incidents, including a devastating attack against Sony Pictures, and data breaches that stole credit card or health data on tens of millions of Americans. 'National emergency': Obama unveiled plans to impose sanctions on hackers after an epidemic of attacks . 'It’s one of the great paradoxes of our Information Age — the very technologies that empower us to do great good can also be used by adversaries to inflict great harm,' he wrote in a blog post on Medium. Obama said cyber attacks - many which originate from overseas - 'pose one of the most serious economic and national security challenges to the United States'. He added it required more than 'diplomacy, law enforcement, and cooperation with other nations and the private sector' to tackle. He wrote: 'It's often hard to go after bad actors, in part because of weak or poorly enforced foreign laws, or because some governments are either unwilling or unable to crack down on those responsible.' Obama said hackers working in China and Russia target America's defense contractors and the systems designed to support the country's troops, while hackers in Iran were targeting banks and North Korea went after Sony. Michael Daniel, special assistant to the president and cyber security co-ordinator, said the new sanctions would 'go after the worst of the worst of malicious cyber actors', while Obama assured people they would 'in no way target the unwitting victims of cyberattacks,' such as people whose computers are hijacked. However, they did not reveal any specific targets, but officials told the Financial Times it could be used against individual hackers hired by companies or countries. Threat: The attacks included last year's Sony pictures hack - allegedly carried out by North Korea. Pictured: The secretive state's leader, Kim Jong-un . Anger: It is said the country was unhappy about the film The Interview (poster, right), which depicted an assassination attempt against the North Korean leader, portrayed by Randall Park (left) They would also not curb the freedom of the internet, Obama stated. But some privacy activists questioned the broad language in the order, saying it could have unforeseen impacts. The order could be interpreted to target investigative reporters, said Marcy Wheeler on the privacy blog Empty Wheel. 'Does WikiLeaks' publication of secret Trans-Pacific Partnership negotiations qualify? Does Guardian's publication of contractors' involvement in NSA hacking?' she wrote. 'I'm generally concerned about this (order) because of the way national emergencies have served as the justification for a lot of secret spying decisions,' Wheeler added. But Paul Rosenzweig of the Chertoff Group, a security consulting firm, said the national emergency language is appropriate. 'The use of "national emergency'" is reflective, I think, of the seriousness with which the administration views the problem — and that's a good thing,' Rosenzweig said on the Lawfare blog. 'What is most notable about the order is how strongly the US is flexing its economic muscle. If access to US markets is of value, the administration is signalling, strongly, that continued access may be conditioned on good cyber behavior. Concern: Some privacy activists questioned the broad language in the order and its unforeseen impacts . However, Obama's advisers were keen to stress how important the new measures were. Lisa Monaco, the President's assistant for homeland security and counterterrorism, wrote in a blog: 'In just the past year, we have seen a significant increase in the frequency, scale, and sophistication of cyber incidents targeting the American people, including everything from large data breaches and significant intrusions to destructive and coercive cyber attacks intended to influence the way ordinary Americans exercise their constitutional rights. 'In many cases, these threats stem from actors overseas using malicious cyber activities to inflict harm on Americans without ever leaving their desks.' Ms Monaco warned 'no one connected to the internet is immune' to the threat, buyt added the sanctions  are 'not a tool that we will use every day' and 'law-abiding companies have absolutely nothing to worry about'.
Barack Obama made announcement following high profile cyber attacks .
Says hackers targeting U.S. from places including Russia, China and Iran .
Critical of 'governments unable or unwilling' to go after 'bad actors'
New order allows treasury to freeze or block assets of those involved .
It is hoped the power will take away the financial incentive behind attacks .