The personal-computing revolution began with a promise: after decades of submission to centralized mainframes, ordinary users were now in control. Buttoned-up IBM loosened its collar, opened its new PC to accommodate hardware and software from a variety of suppliers, and even bought its operating system from a couple of Harvard University dropouts. To reinforce this message, IBM chose as its marketing emblem a look-alike of Charlie Chaplin-timeless hero of the harried underdog. It was a clever choice, and not inappropriate: the PC and other machines like it really did confer upon users a degree of control over information never before available. Twenty years later, technology industries are still promising us autonomy and independence.

But that promise is falling flat. Asserting an unprecedented degree of control over their goods, even once they are in the customers' hands, technology producers are moving to circumscribe the freedom that technology users have long taken for granted. The same powerful trends that have brought leaps in performance-ubiquitous microprocessors, cheap digital storage, and virtually free data transmission-are making possible new ways for technology makers to control users' behavior. These developments reek more of Big Brother than the Little Tramp.

It's not that companies have ill intent. Manufacturers are offering hardware and code they claim will release the full potential of information technology: promoting creativity and productivity while making computing and the Internet secure and reliable at last. Their products address real problems-from brand counterfeiting and piracy, which cost billions, to malfunctioning equipment. But despite the benign intent, some features built into new generations of devices, like the Greek infiltrators in the belly of the Trojan horse, provide openings for intrusion and even conquest. Call it the Trojan mouse.

Measures to control behavior can depend on either accountability or incapacitation. Think of automotive traffic control. Until recently, most communities tried to control speeding with radar-equipped patrol cars. More recently, some towns have shifted to a strategy of incapacitation: they are making speeding physically difficult with increasing use of "traffic-calming" devices such as speed bumps. Police radar is a technology of accountability; it needs the courts to be effective and can be defeated at least some of the time by sensitive detectors. Traffic-calming structures, by contrast, are technologies of incapacitation: they limit passively what people can do with their vehicles.