Jonathan Evans distributed a confidential letter to some 300 top officers at various banks, accounting offices and legal firms warning of the possible attacks, the Times of London said Friday.
The prime minister's office accused China of engaging in state-sponsored espionage targeting integral parts of Britain's economy, using the computer infrastructure of banks and financial services.
This is apparently the first time the British government openly accused China of Internet-based spying, the newspaper said.
Evans' letter warns financial leaders of "possible damage to U.K. 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 letter says British companies conducting business with China are vulnerable to cyber-attacks by the Chinese Army targeting confidential commercial information, the Times said.
Officials with the Chinese Embassy in London denied the accusations and said British authorities failed to notify the office of any complaints.
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