The report to the US Congress said so much sensitive information and research is on computer networks that foreign intruders can collect large amounts of data quickly, but with little risk of detection, according to the Telegraph.
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China and Russia, through their intelligence services and through their corporations, are attacking US research and development, said Robert Bryant, US National Counterintelligence Executive.
Intelligence services, private companies, academic institutions and citizens of dozens of countries target the US. But the report describes Chinese actors as the world's most active and persistent perpetrators of economic espionage.
The report also mentioned that Russia's intelligence services are conducting a range of activities to collect economic information and technology from US targets.
However, the report said although US companies have reported intrusions into their computer networks that originated in China, US intelligence agencies cannot confirm who is behind them.
China is often blamed for cyber attacks, but Beijing authorities continually deny responsibility, saying China is also under constant cyber attack.
At this week's London Conference on Cyberspace, Prime Minister David Cameron said cybercrime costs the UK an estimated £27bn a year. "Every day we are seeing attempts of an industrial scale to steal valuable information from individuals and companies," he said.
UK Foreign Secretary William Hague said: "It is increasingly clear that countries with weak cyber defences and capabilities will find themselves exposed over the long term, and at a serious strategic disadvantage given the apparent rise in state-sponsored attacks."
The UK's soon-to-be-released cyber security strategy is expected to focus on making the UK more resilient to cyber attack and better able to protect its interests. It is hoped the strategy make the public safer online, ensuring the UK is a good place to do business online.