The FBI is warning of a dramatic increase in the number of so-called 'vishing' attacks that entice mobile phone users into giving up personal banking details.

Vishing works in much the same way as phishing. An email or text message is sent to a user asking them to call the target bank to reactivate a credit or debit card.

"On calling the telephone number, the recipient is greeted with 'Welcome to the bank of ...' and [is] requested to enter their card number in order to resolve a 'pending security issue'," the FBI's Internet Crime Complaint Center said in an alert.

The availability of increasingly popular VoIP equipment and open source call-centre software has prompted scammers to set up their own call centres, often employing staff who may be unaware that they are working for a criminal gang.

The FBI is advising users to look up their bank's phone number and call them directly if they believe they have been a victim of a vishing attack.