Criminal gangs are beginning to exploit the internet telephone network to steal bank account and credit card details, it was revealed this week. The fraud has been dubbed “vishing” because it is similar in technique to phishing, the scam that uses bogus e-mails and websites to elicit bank details from unsuspecting internet users.

The fraudsters are using cheap telephone calls through voice-over-internet protocol (VoIP) to bombard thousands of people with automated messages saying that their credit card or bank details have been used illegally. The messages implore the recipients to call a bogus number to have their details updated. When the unsuspecting victim phones the number, it is answered by a computer-generated voice that tells the caller to tap in card details and security information. By doing so, the caller gives the fraudsters all the information they need to empty the caller’s account.

Paul Henry, an executive at Secure Computing, the American internet security company that highlighted the scam, says that criminals are using VoIP because the calls are either free or very cheap. The perpetrators are also taking advantage of the banks’ own security measures. “It is a normal procedure when calling a credit card provider to be asked to enter your 16-digit credit card number before given the opportunity to speak to a representative,” he says.

The fraudsters are also using VoIP because they can use the technology to “spoof” the telephone number they are calling from. Mr Henry says that the ability to make the call look like it is coming from a legitimate bank or credit card company helps the fraudster to disarm the suspicions of the victim.

To prevent systems from being exploited by these spoofers, many VoIP providers, including Babble and Skype, block customers’ outgoing calling line ID. This means that recipents cannot be fooled into thinking that they have been called by someone they haven’t. However, not all VoIP providers have this policy, so there is no way of knowing for sure whether a call from a VoIP network is from a legitimate or spoofed number.

Allan Howes, managing director of babble.net, a VoIP provider, says that consumers have to be vigilant. “The safest thing to do if you receive a call that you are unsure about is to say that you will call back on the company’s main advertised telephone number.”

Some industry watchers believe that as VoIP enters the mainstream, users could become bombarded with auto- dialled or spam calls because there will be no cost to the caller. The industry describes these type of unwanted voice messages as “spit” calls.

Mr Howes says: “Most VoIP providers are working on developing spit filters in the same way that e-mail providers have spam filters.”

Phillip Parker, a project manager from Warwick has used VoIP for about 18 months. He says: “That fraudsters can spoof numbers with VoIP is a concern but I have not yet received a vishing call. I tend not to answer calls where I don’t recognise the number. In the time that I have used VoIP I have not noticed an increase in the number of spam calls.”