The number of Trojans targeting the Symbian smartphone platform is double the number previously discovered, mobile anti-virus vendor SimWorks has warned.

The company has uncovered a total of 52 new Trojans, mostly hiding inside hacked versions of popular games for the operating system. The total number of malware programs believed to affect Symbian has now reached just over 100, and has risen dramatically in recent months.

The company didn’t give details of how it had discovered so many new Trojans in such a short space it time.

Nokia Series 60 phones and smartphones running Symbian OS version 6.1 are believed to be at risk. Other phones running Symbian, such as the Sony Ericsson P900/910 and Motorola A925/1000 are not on the list.

Programs in which Trojans were discovered included BitStorm, BugMe!, Cosmic Fighter, 3D Motoracer, and Splash ID. The Trojans also appear to be more malevolent that those discovered to date.

"Previous mobile viruses have either been able to spread but cause no harm or, alternatively, to cause significant harm but not able to spread," said Aaron Davidson, CEO of SimWorks.

The new family of infected programs had the potential to cause serious harm to people using Symbian devices, however. "Every other file could contain something that could cause your phone to be corrupted, requiring a factory reset or worse, and the loss of all your contacts and other data."

The company admitted that the Trojans had not been discovered in the wild, and there was no evidence that they had infected so much as a single Symbian phone. They stated that although the risk was currently theoretical, it should still be taken seriously.

Graham Cluley of anti-virus vendor Sophos was undecided on the significance of the discovery. "Our labs haven’t received any samples of these yet. It is possible that the way they count these things is different form the rest of the industry," he said.

He remained sceptical that the current threat was of any real worry, though he agreed this might change in the future. "We have never received a single report of any infection on Symbian from our customers – not a single one. This could just be one guy in his back bedroom."