VeriSign has expanded coverage for its VIP identity protection service for mobile handsets.

The update will expand the free service to more than 90 handsets, including BlackBerry and iPhone devices.

VIP allows a user to receive new passcodes on their handsets that then serve as temporary access codes for online retailers. The software is similar to the key fob device used by VeriSign and other vendors to prevent online account theft.

In the US, the VIP mobile software will be supported on handsets using Sprint, AT&T and Verizon networks. O2 and Vodafone will support the service in the UK.

VeriSign hopes that by expanding the reach of the mobile software, users will take a greater interest in the VIP programme.

"Transforming mobile phones into VIP credentials is a key element in the effort to give two-factor authentication a broader footprint among consumers and enterprises," said Fran Rosch, VeriSign's senior vice president of authentication products and strategy.

"VIP Access for Mobile is part of our strategy to make VIP strong authentication ubiquitous by making it increasingly easy for users and enterprises alike to adopt and use."