Security researchers have warned that greater numbers of mobile malware attacks could be on the horizon.

Thus far, most malware programs targeting wireless devices have been proof-of-concept threats or have required large amounts of end-user interaction to deliver their payloads, but experts contend that malware writers are unquestionably ramping up their efforts in the space.

As part of its semi-annual (twice yearly) Internet Security Report, published March 19, researchers at Symantec cited mobile threats - specifically those that use wireless messaging systems to lure end-users to poisoned URLs - as a growing concern for 2007.

In 2006, mobile threats of note included the Mobispy attack, the first known handheld spyware program tracked by security researchers.

According to anti-virus applications maker F-Secure, there are already more than 370 different wireless threats in the air, including attacks that attempt to delete data stored on handhelds and even record end-users' phone calls.

Over the next year, security vendors expect to see new threats aimed at wireless transactional systems and users of less sophisticated handheld hardware.

"As the addressable market for smartphones expands, there will be more attacks, as malware activity always moves to the areas of greatest impact," said Jan Volzke, head of marketing for mobile security at McAfee. "There will also be more viruses written to attack simpler, Java-based handhelds, as there are far more of those devices in people's hands today."