LONDON — The head of Britain's domestic spy agency has warned that China is spying on the computer systems of British corporations, a newspaper reported Saturday.

The Times of London said MI5 chief Jonathan Evans sent a letter this week to 300 executives and security chiefs at banks, accountancies and legal firms, warning them that they were under attack from "Chinese state organizations" over the Internet.

The newspaper said the letter had also been posted on a secure section of the Web site of the government's Centre for the Protection of the National Infrastructure.

It included ways of identifying Chinese "Trojans," software designed to hack into a computer network and feed back confidential data, the Times said.

The government Home Office, which oversees MI5, said it would not comment on private correspondence.

British Prime Minister Gordon Brown said last week that he would make his first visit to China as premier in January.

China has steadfastly denied it is engaged in any cyber crime and said its networks also have been targeted.

A spokesman for the Chinese Embassy in London did not immediately return a call seeking comment on the Times report on Saturday. And telephone calls to the Beijing Foreign Ministry and a duty officer's mobile phone went unanswered late Saturday.

Computer experts have blamed hackers linked to the Chinese military for cyber attacks on the U.S. Pentagon, the British Parliament and the German chancellery.

A report issued in the United States by security software vendor McAfee Inc. on Thursday, based on McAfee research and input from security experts with NATO, the FBI and other intelligence organizations, said hackers in China are believed responsible for four out of five major cyber attacks on government targets in 2007.

Chinese Foreign Ministry spokesman Liu Jianchao said at a briefing Thursday that "China has also been attacked by hackers of some countries, so the Chinese government attaches great importance to and participates in the international law enforcement cooperation in this area."

Experts have said that China is home to a large number of insecure computers and networks that hackers in other countries could use to disguise their locations and launch attacks.