MILLIONS of internet users could unwittingly give their bank account details to criminals via a new scam.

Up to half of home broadband customers may be susceptible to a type of attack known as 'drive-by pharming', experts warn.

Simply by viewing a rogue website, without downloading any software, they could be targeted.

Visiting the site activates a system that re-routes the user away from his normal server. Without realising it, victims are connected to a new server, controlled by criminals, who can direct them anywhere they like on the net.

Next time they log on to look at their bank account or pay a bill, the new server directs them to a replica site which could be an exact copy of the real one.

The victim's user name and password can then be stolen, allowing the attacker to access the `real' bank site and rob the account.

Broadband routers employ different systems and not all are vulnerable to drive-by pharming.

But experts say up to 50 per cent of popular wireless routers could be at risk because they are so easy to access.

Software specialist Dr Zulfikar Ramzan said: "The attacker will try to get you to go to his website.

Gossip

"It might be a new video of Britney Spears with her bald head, gossip, celebrity pictures or pornography. All you have to do is look at it. They say curiosity killed the cat - now it may also kill your bank account."

It is not known whether anyone has yet fallen victim to `drive-by pharming', but Dr Ramzan said he felt it essential to warn people.

The scam involves the use of a JavaScript code to change the settings of a user's home broadband route, which provides the link with the server.

One way to guard against it was to change the default internal password used by the router, said Dr Ramzan.

Users should be wary of clicking on links or sites that seem in any way suspicious, he said.

He added: "We're working night and day to find ways of defending against these threats.

"You have to keep one step ahead and be able to react quickly."

Existing security solutions that only protect a user's home computer system cannot prevent attacks such as drive-by pharming.

His US firm is looking at new systems that can monitor the behaviour of a program and spot when it is acting strangely.

"That could enable us to counter threats we haven't even seen yet, but the problem is how to prevent it being triggered by legitimate activity," he said.

Expert Prof Markus Jakobsson said the dangers highlighted the human Achilles heel in internet security.

He added: "To a large extent, it's a social threat, with people being tricked to install things or de-activate countermeasures. It's becoming much more sophisticated and prevalent - and it's becoming much more of a complex threat."