"If you look at terrorism, if we'd relied on prosecution, we would have had lots of incidents by now. We have to rely to a very significant extent on actually disrupting the activity while in course."

It was often difficult to establish who was behind the attacks, she said, adding: "They're fearless. They don't actually believe they're going to be caught.

"There are both private criminals, there are organised networks, and there are also, very clearly, state players. I think it's very clear that we do take the issue of the international rules of the game very seriously."

Baroness Neville-Jones went on: "You need to be able to take action to stop the effects of it well before you have necessarily achieved a degree of certainty about attribution.

"I don't wait before I take action. Action means that I've actually got to close my defences. A lot of modern security is about reducing vulnerability."

She added: "It's a bit like terrorism in that, the more you know, the more frightening it becomes. It isn't that the situation has changed, it's that you know more about it."

The report, by information consultants Detica for the Cabinet Office, showed cyber crime costs the UK almost £1,000 every second.

But the Cabinet Office said that "in all probability, and in line with worst-case scenarios, the real impact of cyber crime is likely to be much greater".

Many firms are reluctant to report cyber attacks out of a fear it would damage their reputation.

Theft of intellectual property, such as designs, formulas and other company secrets, from businesses costs £9.2 billion, with firms specialising in pharmaceuticals, biotechnology, electronics, IT and chemicals being hit hardest.

Industrial espionage, including firms spying on each other, costs £7.6 billion.

Cyber crime also costs citizens £3.1 billion a year and the government £2.2 billion a year, the report said.

Cyber attacks on the UK's information technology systems were identified in last year's Strategic Defence and Security Review (SDSR) as one of the four most serious threats to national security, alongside terrorism, natural disasters and major accidents.

Backed by £650 million in new Government funding announced in the SDSR, the National Cyber Security Programme will develop means of responding to threats from states, criminals and terrorists.