Cyber criminals have created a highly sophisticated Trojan virus that steals online banking log-in details from infected computers.

The Clampi virus, which is spreading rapidly across hundreds of thousands of computers in Britain and the United States, infects computers when users visit websites that host a malicious code.

Once on the computer, the virus sits unnoticed until the user logs on to bank, credit card or other financial websites. It then captures log-in and password information and sends it to a server run by the attackers. They can then tell the compromised computer to send money to accounts that they control, or they can buy goods with the stolen credit card details.

The trojan has a list of more than 4,500 finance-related websites that it monitors, including British high street banks. Security experts warned that it was one of the stealthiest and most pervasive threats to computers using the Microsoft Windows operating systems.

Orla Cox, security operations manager with Symantec, the online security company, said: “Clampi is a complex threat. People are only just beginning to understand how it operates.”

Researchers have found that the list of sites that Clampi is monitoring includes banks, credit card companies, online casinos, e-mail, wire transfer services, retail sites, utilities, share brokerages, mortgage lenders and government sites.

Ms Cox said: “The first big wave was in the US in July, but it is spreading around the world, particularly English-language countries. We have seen samples of it targeting UK high street banks. There is potential for another wave to come.”

It is estimated that more than 1,000 out of 40,000 or more infected computers have been in Britain. Only computers running Microsoft Windows are affected. Most of the infections seem to have occurred among small and medium-sized businesses, many of which have been reluctant to reveal how they have fallen victim.

In America, $75,000 (£46,000) was stolen in July from Slack Auto Parts, a car parts supplier in Gainesville, Georgia. In August, criminals used Clampi to steal online banking details for the public school district in Sands Spring, Oklahoma. The attackers then submitted a series of false payroll payments, totalling more than $150,000.

The attack was one of a series on American schools in which criminals hired unsuspecting money mules — people who transfer money or fraudulently obtained high-value goods — to receive the transfers of stolen cash and then wire the money out of the country. Cyber criminals stole more than $700,000 from the Western Beaver School District in 74 fraudulent electronic transfers, The Washington Post reported.

Clampi is one of a new wave of viruses to target the online banking system. Its emergence came as security experts warned that malicious websites hiding trojan viruses were no longer confined to sites such as gambling and pornography.

A recent report by IBM security systems found an increase in malicious content such as viruses on trusted sites, including popular search engines, blogs, online magazines and mainstream news sites. The number of links to malicious web pages rose by more than 500 per cent in the first half of this year. Last week, attackers placed a virus in an advert on the website of The New York Times.

Trojan viruses such as Clampi accounted for 55 per cent of all new malicious software in the first half of the year, IBM said, up from 46 per cent for the same period last year. Researchers say that variants of Clampi — also known as Ligats or Ilomo — have been around since 2005, but the new version appears to be spreading more quickly.

Heading off hackers

Do not click on suspicious links to unknown sites within e-mails, instant messages or social networking sites

Be cautious about doing business with unknown e-commerce sites and always use a credit card, not a debit card

Install a comprehensive security solution and keep it up-to-date

Use a security solution that offers browser protection and a website rating service Browser protection will block questionable downloads from getting on to your computer, and website rating services can warn you if a site is infected

Secure your wi-fi connection with a strong password to ensure that others cannot connect to your network and access data stored on your computer

Any user whose system has been infected by Clampi should immediately change any and all passwords used on that system for any websites, but particularly financial credentials

Source: Symantec

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