Jonathan Evans, head of MI5 sent a letter this week to 300 banks and accounting and law firms. A summary posted on a secure Web site described the letter as "warning them of the electronic espionage attack," The Times of London said.
"The contents of the letter highlight the following: the director-general's concerns about the possible damage to UK business resulting from electronic attack sponsored by Chinese state organizations, and the fact that the attacks are designed to defeat best-practice IT security systems," the summary said.
The Web site maintained by the Center for the Protection of the National Infrastructure provides access for businesses like telecommunications companies, banks, and water and power suppliers that play a critical role in the functioning of the country.
Prime Minister Gordon Brown is to make a state visit to China early in 2008, which could be complicated by diplomatic fallout from the MI5 warning.