ZeuS - a type of sophisticated malicious computer program - has been used to harvest millions of lines of data from affected machines. It records online bank account details and passwords, credit card numbers and other personal information, before causing the computer to forward the data to servers under the control of the distributors.

The Trojan has been implicated in a wave of successful online banking assaults on US small businesses over the past several months and a $6 million commercial account heist on 20 European banks in the summer of 2008.

The PCeU officers arrested a man and woman, both aged 20 years, in Manchester on 3 November for offences under the 1990 Computer Misuse Act and the 2006 Fraud Act. The unit says these are Europe's first arrests in the battle against ZeuS.

Both suspects were interviewed by detectives and have been bailed for further in-depth enquiries to be completed.

Detective inspector Colin Wetherill, PCeU, says: "The ZeuS Trojan is a piece of malware used increasingly by criminals to obtain huge quantities of sensitive information from thousands of compromised computers around the world. The arrests represent a considerable breakthrough in our increasing efforts to combat online criminality."