A virus targeting online bank accounts has hit thousands of online banking customers, although the name of the bank has yet to be disclosed.

The ‘Trojan Horse’ virus, created by hackers and originating from a server in Eastern Europe, has stolen £675,000 from 3,000 accounts at the bank. The name of the high street bank has not yet been handed over to police.

According to computer experts, the virus is still progressing. The Trojan virus – which cannot be detected by traditional anti-virus software – can install itself on computers while victims are browsing legitimate sites on the internet.

The virus, known as a Zeus v3, then copies the passwords and usernames of customers’ online banking accounts and, if there is more than £800 in the account, transfers their funds.

The money is transferred to the bank accounts of “money mules,” innocent people recruited to use their own bank accounts to funnel money through. From there, the money is transferred to accounts in other countries that are controlled by the hackers.

In a clever twist, the virus also gives customers a false bank balance screen so they are unaware the money has been stolen.

A spokeswoman for Financial Fraud Action UK said the use of Trojans or malicious software to steal cash was “nothing new”.

“Bank systems are hard to attack so they’re having to go through the easier link in the chain, which is the customers,” said the spokesperson.

“They’re hoping customers aren’t taking security precautions. We’ve been seeing this for the last few years and we’re constantly urging people to protect their computers to try to mitigate the risk of becoming a victim.”