(FORTUNE Magazine) – Somewhere in the inner circle of hell where virus writers and spammers maintain their offices, a young entrepreneur is crafting a marketing campaign for pills that will shrink your penis and enlarge your mortgage payments--er, wait, it's the other way around. The virus writer in the cubicle next to him is working on a new kind of digital worm that will make your life miserable and cost businesses a couple of billion dollars in lost productivity.

Sound familiar? Of course. But this time the viruses and spam won't be aimed at your desktop computer. Instead, the bad guys are planning to target your mobile smart phone, your wireless e-mail and instant-messaging device, and maybe even your home security system or your car. Until now--in the U.S. at least--wireless devices like cellphones have been blissfully free of the vile bits that clog and clobber our desktop and laptop computers. But things are changing fast. Sales are growing for e-mail-and web-capable smart phones. These devices invite text and instant messages into your pocket. And as of November, when the Federal Communications Commission began allowing people to transfer their home numbers to their mobile phones, cellphones have become more vulnerable to the annoying speed-dialed solicitations that interrupt our dinner hour.

Of course, you can reduce the number of junk calls you get by signing up for the new federal Do Not Call registry. But junk calls may be the least of our worries. Soon we'll have smart phones and BlackBerries that are constantly connected to broadband data and voice networks and to one another. Our offices, houses, and cars will bristle with chips that communicate wirelessly over the Internet Protocol (IP) network. Elevators, security systems, home appliances, and even the clothes on the rack at your favorite department store will have sensors that relay vital information to central computers. To talk to each other, those smart devices will use a common data communications infrastructure. And as experience with the Internet has taught us, when bad guys see millions of intelligent devices connected on a common platform, the temptation to create viruses, worms, and spam becomes too strong to resist.

What can we expect as handhelds become, as they say, a target-rich environment? Your smart phone rings with a call offering a unique chance to help a deposed African dictator transfer millions to your bank account, or vibrates with e-mail touting Viagra. Or it beeps with an obscene and frighteningly detailed Bluetooth text message from some masher seated 20 feet away. Or--this is merely a fear right now--a text message triggers code that steals your personal information, causes your phone to broadcast dozens of SMS messages that cost you 20 cents a pop, or tricks you into placing expensive toll calls to an area code somewhere in Armenia. In Japan, where the smart-phone future is already rolling out, the average user of the popular DoCoMo iMode system receives nearly two dozen spam text messages a day, the company concedes. The biggest danger, says Sunil Misra, chief security advisor for Unisys, could come later on, as sophisticated communications devices are embedded in autos and other "real time" machines. Misra explains, "If you have a device in a car that is wirelessly connected to the Internet by a high-speed always-on connection, and it's sharing a network with a device in the car that controls the brakes, well, a virus can become life-threatening."

How soon will the misery begin in the U.S.? "It's hard for anyone to say when we're going to see a major cellular worm or a wireless virus," says Laura Garcia-Manrique, a group product manager for Symantec, a Cupertino, Calif., maker of antivirus software. The first virus to attack the Palm operating system, used by the majority of smart handheld devices today, was identified in 2000, she says, but things have been relatively quiet since then. All the same, "there are things that are doable today that were not doable three years ago." Symantec has just released a new version of its antivirus software for smart phones and connected handhelds, and other antivirus companies are doing the same. Cellphone providers, meanwhile, are installing virus and spam filters on computers in their networks. And in the labs, says Misra of Unisys, technologists are developing safeguards for networks that will "use the human immune system as a model for how to detect anomalous behavior and respond."

We could thank them for that. Of course, we could also give our smart phones a lobotomy.

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