A computer virus has been used by criminals to steal £675,000 from the online bank accounts of high street banking customers.

The money was stolen from July onwards from the customer accounts of an unnamed bank using the Zeus virus, which checks account balances, drains out deposited money and shows customers a fake balance leaving them unaware of the fraud.

Bradley Anstis, vice president of technical strategy at a specialist firm dealing with online fraud called M86 Security,  said: “This is an extremely sophisticated version of the virus and it cannot be detected by traditional security software”.

However, a spokeswoman at Financial Fraud Action UK, which deals with fraud in the banking sector, said customers shouldn’t be overly concerned about the recent happenings: “This has the potential to worry a lot of people, which is not founded. The bank wants to make sure everything is being done behind the scenes to protect customers. It wants to make sure customers aren’t unnecessarily alarmed”.

She added that the reason the bank had not been named was to prevent customers from being unduly disturbed. She confirmed that anyone affected would be reimbursed.

The only bank to comment on the virus was HSBC. A spokesman said: “There are millions of viruses, and other malicious software. We urge people to take basic measures to protect themselves from virus attacks. Any customer who is the victim of fraud will be reimbursed by HSBC”.

M86 Security tracked the crimes back to a server based in Eastern Europe.