CREDIT card details and passwords stolen from UK computer users are among thousands of confidential files recovered from a computer in the United States.
The Metropolitan Police Computer Crime Unit says the data was stolen from more than 2,300 computers by the use of a virus.
Police estimate that around 83,000 files in the UK have been targeted by the hackers, but thousands of computer users around the world may have had information stolen, including e-mail addresses, passwords and credit card numbers.
The details were harvested from the computers by a type of malicious code known as a "backdoor".
It is not yet known how many computers have been infected, but officers are taking steps to notify UK victims.
Banks and other online services, including internet service providers, are also being alerted.
A police spokesman said: "Identity theft by computer viruses is on the increase."
Police are advising computer users to update antivirus programs regularly and scan their computers to lessen the chances of becoming a victim.