Cape Town – Britain is seeing about 70 sophisticated cyber espionage operations a month against government or industry networks, British intelligence has told the BBC.
GCHQ director Sir Iain Lobban said business secrets were being stolen on an "industrial scale".
Foreign hackers have penetrated some firms for up to two years, he said. And he denied that his organisation had broken the law in receiving information from the Prism spy programme.
Foreign intelligence services are behind many of these attacks, according to Britain's Security Service MI5.