Consumers with an internet-enabled mobile phone have been urged to make sure that any data it contains is secure.
According to research by Experian, the personal information stored on smartphones can be "like gold dust" to an identity thief.
However, the organisation believes that people who use public wi-fi networks could be effectively putting this data "on a plate" for criminals.
Indeed, figures from Experian showed that nearly one in five smartphone owners use unsecure public wi-fi hotspots to carry out online banking.
Statistics also revealed that nearly two-thirds of people with a high-end device use it to send and store emails.
Experian warned that this means highly sensitive personal information, such as Pins, passwords, bank account numbers and credit card details, could be extremely vulnerable.
Peter Turner, managing director of Experian Interactive, commented: "A criminal can use this information to masquerade as the phone's owner, drain his or her accounts, run up debts in their victim's name and even open new accounts."
The study by Experian also showed that users of social networking sites could be especially vulnerable to identity thieves.
This, it said, is because people's profiles on sites such as Facebook often contain information that form the basis of website passwords, such as their date of birth and the name of their first school.
Experian noted that 53 per cent of consumers with a smartphone use their handset to access social networking sites.
Mr Turner added that people may be unaware they have fallen victim to an identity thief until demands for payments for services they have not used start to appear.
This comes after research by Good Mobile Phones found that more than two-thirds of people who sell on their handset fail to clear the personal data it contains beforehand, reports Computer Weekly.
The organisation said this means they could be vulnerable to identity thieves, particularly as text messages and the phone's internet browser history could contain sensitive pieces of information.