Government and industry networks are the target of around 70 sophisticated cyber espionage operations a month, British intelligence has said.
GCHQ director Sir Iain Lobban told the BBC that business secrets were being stolen on an "industrial scale", while offshore hackers have penetrated some firms for up to two years.
Speaking to Radio 4, he commented: "We started a couple of years ago thinking this was going to be very much about the defence sector but really it's any intellectual property that can be harvested."
British businesses are now waking up to the threats of cyber espionage, with Sir Michael Rake, chairman of BT and president of business lobby group CBI, stating that the dangers are real and doing financial and reputational damage.
Firms in the ICT, engineering and educational sectors are most likely to get targeted, according to GCHQ data - although the majority of the attacks do occur on government and defence networks.