The thefts came to light when just one US computer was seized in the US. It contained personal details from 2,300 computers in the UK. Amongst the details were credit card numbers, email addresses, passwords and details of transactions conducted online.
The Met is now trying to identify and contact everyone affected by the scam. "The information has been harvested from the computers by a type of malicious code known as a back door," said a statement from the Met's Computer Crime Unit.
"It is too early to establish at this early stage how the computers have been infected. However, there are thousands of computer users worldwide who have had their computers compromised and data stolen," said the statement.
The Met has emailed everyone whose data has been stolen, but is said to be worried because some users clearly think that the emails are a hoax. The force is urging people to get in touch with the Met if they have received one of the emails.
Home computer crime is a growing problem. A recent report from anti-virus firm Symantec claimed that hackers and online criminals are increasingly turning their attention away from well-protected corporate networks and towards less secure home computers. The company estimates that 86% of attacks are aimed at home computers.
A just-finished BBC experiment has found that home computers are attacked as much as 50 times in one night. The BBC set up a 'honey trap' test PC and logged the attacks by hackers that it suffered.
It found that a home PC suffers at least an attack an hour, one of which was an attempt to take control of a computer and turn it into a 'zombie pc'.