VIRUS can wreak havoc on computer files, hard drives and networks, but its malicious effects tend to be measured in wasted time, lost sales and the occasional unfinished novel that evaporates into the digital ozone. But what if viruses, worms or other forms of malware penetrated the computers that control ever more crucial functions in the car?

Could you find yourself at the wheel of two tons of rolling steel that has malevolent code coursing through its electronic veins?

That frightening prospect has had Internet message boards buzzing this year, amid rumors that a virus had infected Lexus cars and S.U.V.’s. The virus supposedly entered the cars over the Bluetooth wireless link that lets drivers use their cellphones to carry on hands-free conversations through the cars’ microphones and speakers.

The prospect is not so implausible. A handful of real if fairly benign cellphone viruses have already been observed, in antivirus industry parlance, “in the wild.”

Still, a virus in a cellphone might muck up an address book or, at worst, quietly dial Vanuatu during peak hours. But malicious code in cars, which rely on computers for functions as benign as seat adjustment and as crucial as antiskid systems that seize control of the brakes and throttle to prevent a crash, could do far more harm.

The Lexus tale, based on murky reporting and a speculative statement by Kaspersky Labs, a Moscow antivirus company, seems to have been unfounded. “Lexus and its parent companies, Toyota Motor Sales USA Inc. and Toyota Motor Corporation in Japan, have investigated this rumor,” the carmaker said in a statement last month, “and have determined it to be without foundation.”

But the question lingers: Could a car be infected by a virus passed along from, say, your cellphone or hand-held computer? Or worse, by a hacker with a Bluetooth device within range of the car’s antennas?

The short answer is, not yet.

“Right now this is a lot of hype rather than reality, the idea that cars could be turning against us,” said Thilo Koslowski, a vice president and lead analyst for auto-based information and communication technologies at Gartner G2, a technology research firm. “We won’t see John Carpenter’s ‘Christine’ becoming a reality anytime soon.”

But Mr. Koslowski and others are quick to point out that the elements for mischief are slowly falling into place:

First, vehicles are increasingly controlled by electronics – to the point that even the simple mechanical link between the gas pedal and engine throttle is giving way to “drive by wire” systems.

Second, more data is being exchanged with outside sources, including cellphones and real-time traffic reports.

Finally, the interlinking of car electronics opens up the possibility that automotive worms could burrow into a memory storage area in ways that engineers never imagined.

Since the early 1990’s, the various computers that manage a car’s engine, transmission, brakes, air bags and entertainment systems have been increasingly linked in networks much like the ones that offices use to let workers share printers, scanners and backup storage drives. Benefits of interconnecting the electronic devices include less wiring – a luxury car can contain miles of copper cables – and reduced weight, an important factor in improving performance and fuel economy.

Less obvious are the advantages of having the components communicate: an antiskid system, designed to help keep a car from spinning out of control, links sensors in the steering, brakes and throttle, and can effectively seize control from the driver.

Other systems in which computers essentially take over, if only for a second, include emergency-brake assist, which provides maximum braking force when sensors detect the need for a panic stop, and “active steering,” a feature now exclusive to BMW in which computers can compensate for a driver’s recklessness.

The latest versions of in-car information systems, known as telematics, include the ability to diagnose vehicle maladies. General Motors’ OnStar can forward readings from sensors throughout the car for troubleshooting, a process called remote diagnostics. (All G.M. cars will include OnStar by the end of 2007.)

New York Times – 13 March 2005 – By Tom Zeller Jr. and Norman Mayersohn