You don't have to be Paris Hilton to worry about strangers getting into your cell phone. Just as mobile handsets take on functions once reserved for personal computers, they also inherit PC-like headaches--like mobile viruses.
The first virus for Symbian operating system-based phones, Cabir, was found in the wild last June. Much like a living organism, Cabir spreads through the air from host to host, using a phone's Bluetooth transceiver to locate new victims. Bluetooth is your cell phone's underused short-range wireless networking capability. Travelers who hop from continent to continent have been unwitting carriers of Cabir: According to antivirus vendor F-Secure, Cabir has been spotted in 17 countries, from South Africa to Singapore.
Once your phone is infected, strangers can add anonymous messages to your phone book (an exploit called "bluejacking"), steal your contacts and calendar data (bluesnarfing), monitor your movements (bluetracking), or listen in on your conversations (bluebugging). Mostly, however, Cabir drains your phone's battery as it scans for other handsets to infect.
F-Secure's Mobile Antivirus and Trend Micro's Mobile Security can detect and eradicate Cabir; you can also change your phone's Bluetooth settings so that it's "undiscoverable." Check your phone's on-screen menus to figure out how to access the settings. You'll still be able to use a Bluetooth headset and other peripherals, but Cabir-infected handsets won't be able to find your phone.
Because of the limited number of phones using the Symbian OS, Cabir isn't considered a huge threat. But the same folks who wrote Cabir have created a (mild) virus that attacks phones using the Windows Mobile operating system. As more Windows smart phones enter the market, you can expect more--and more virulent--mobile malware to appear.