A network of around 100,000 machines has formed a “botnet” - a collection of software agents, or robots, that run autonomously and automatically from infected machines.

The hijacked information includes login details for online banks, credit and debit card numbers and other passwords.

The contaminated machines have been infected with a Trojan [a piece of software that allows unauthorized access to the user's computer system] known as Zeus.

Researchers at Trusteer were able to identify the geographical location of victims after they gained access to the command and control centre of the Trojan network using the fraudsters' own data to assess the botnet and determine that it actually targets the UK.

Once infected, computers are effectively under the control of the cyber criminals. Allowing them to monitor and collect all kinds of information, including bank details. This later allows the criminals to sign on to the account and wire money out.

The scam is difficult to identify but people should be suspicious if there was any change in their bank's login procedures or they were prompted to resubmit their password and other details.

The Metropolitan Police central e-crime unit has been alerted to the scam and is investigating.