New viruses targeting Symbian smartphones have surfaced, according to NetQin, which develops security software for mobile devices.

Two Symbian operating systems are vulnerable: S60 platform 3rd Edition, aka Symbian OS 9.1, as well as S60 5th edition, aka Symbian OS 9.4. The operating systems run a number of smartphones from such manufacturers as Nokia, Samsung and Sony Ericsson.

Dubbed ShadowSrv.A, FC.Downsis.A, BIT.N and MapPlug.A, the viruses come hidden in games designed for Symbian smartphones. Once the games are run, the virus executes, giving the virus writer full control over the devices, said NetQin. In other words, the smartphone becomes part of a botnet, and can be used to launch further attacks on other devices.

In addition, according to NetQin, "these viruses will either send messages to all the contacts of the address book directly, or send messages to … random phone numbers by connecting to the server." The messages sent by the virus contain URLs, purportedly to such content as World Cup video on demand or popular television shows, but which really link to websites hosting the virus. To cover its tracks, the virus deletes any messages it sends from a user's outbox and SMS log.

NetQin estimates that 100,000 mobile phones worldwide are vulnerable to the virus.

Smartphones being infected by viruses isn't a new threat, and malware aimed at smartphones continues to mature. For example, in late 2009, researchers, discovered the iKee botnet, which targeted jailbroken iPhones, backed by command-and-control functionality to press these iPhones into the service of a botnet.

Even so, stumbling into a virus by downloading a mobile application is a relatively new threat. "The explosion of mobile applications has made smartphones an enticing target for virus authors," said Lin Yu, CEO of NetQin, in a statement.

Driven by financial incentives, "many security threats that were once only spread on PCs, such as botnets, are now moving to mobile devices," he said.

These financial incentives may include making phones spend money on services controlled by attackers. For example, last month, Donato Ferrante at Sophos wrote a blog dissecting a different piece of Symbian malware, Troj/SymbSms-A, which spreads via an SIS archive file. Its purpose appears to be to send messages to a premium-rate Russian phone number until the infected smartphone runs out of credit.