ONLINE banking customers could face heavy losses because they don’t realise the small print in their agreements means they have to protect their computers against fraud.

The number of Britons affected by bank fraud has soared in recent years.

Ricky Gervais, the comedian, is one high-profile victim. Two fraudsters were jailed last month for using confidential bank details to steal £200,000 from his account. Cheekily, they used a photograph of Gervais in his award-winning role as David Brent of The Office.

And people with online bank accounts are becoming increasingly common targets as anti-fraud measures make it harder to steal from credit-card users.

Most banks will give you a refund if you lose money to a fraudulent attack on your internet account. However, the small print of banks’ terms and conditions often states that, in return for this financial protection, customers must keep the firewalls and anti-virus software on their computers up to date.

Dave Martin of Logica CMG, an IT consultancy, said: “If you read the terms and conditions of most online banks, you will see that the fraud protection agreement requires you to stay up to date with firewall and virus protection advances.”

Banks want customers to use the latest security packages because the computer hackers employed by criminal gangs are constantly coming up with more sophisticated ways to gain access to accounts.

Trojan programs, which capture details by monitoring your keystrokes, are a favourite with the fraudsters.

The latest version, which can be caught through receiving an e-mail, visiting a website or downloading software, targets customers of Barclays, Halifax, HSBC, Lloyds TSB, Nationwide, NatWest, Abbey’s Cahoot brand and Co-operative Bank’s Smile.

It is particularly crafty because it lies dormant until you try to access an internet banking account and then sends you to a fake website, designed to look like the real thing.

Any security details — such as passwords and account numbers — you type in are then logged by the software, picked up by the hackers and used to remove money from your account or steal your identity.

Wessel van Rensburg of Lycos UK, an internet portal, said: “One of the most common tips given to help people avoid internet banking fraud is always to key in the web address of the bank, rather than clicking on a link. However, that will not help with this particular trojan, meaning it could prove to be very dangerous.”

Online bank customers are also likely to be targeted with so-called “phishing” e-mails, which appear to be from your bank and attempt to dupe you into disclosing personal security information.