Spying on someone by hacking into his webcam is disturbingly easy. Why don't more people do it?

Still, webcam espionage isn't very common. Most scammers are interested in money, and video of someone's slack-jawed mug isn't going to yield much cash. "Most stuff you'd capture on a camera, they've already posted on Facebook," says Kevin Haley of Symantec Security Response. *Even if you did have hundreds of hours of video and audio capturing someone's conversations, it's a lot harder to index and search than written information. (Some programs solve this problem by activating the camera only if they sense movement.) If it's profit the hacker wants, the contents of the computer are much more valuable than whatever's happening in front of it.

If someone hacks into a webcam, therefore, it's usually a targeted attack. Pure creepiness is one motivation. A 15-year-old girl in Texas reported in 2004 that a hacker who took over her computer would eject the disk drive and say things like, "I like your shirt."

Then there's spying on people you'd like to keep an eye on, such as, say, your spouse. One could see this being useful for private investigators, though PIs I spoke with say they don't know of anyone hacking into webcams as part of their work. "The technology is there for it to happen," says Charles McLaughlin, a PI in Andover, Mass. "But in the private sector, although there are some characters willing to break the law, most reputable PIs don't." You might get away with it if you install the spyware own your own computer—say, the one in the bedroom—but even that gets into shady legal territory.

More threatening than video is audio. By accessing a computer's microphone, you turn the computer into a bug. It's also more clandestine than video, since the microphone is always on and there's usually no light to tip you off when it's recording. "The mic thing worries me a lot more," says Chris Wysopal of the security firm Veracode. "Unless you can lip-read, [video alone] isn't that useful."

So how do you prevent someone from spying on you? The usual Internet hygiene applies. Don't click the weird attachment your computer-illiterate relatives send you, update your antivirus software regularly, and so forth. If you want to be really cautious, the best solution is the simplest: Put a piece of tape over the camera. It may be the laptop equivalent of the tinfoil hat, but it's the only way to absolutely guarantee privacy. The microphone is trickier, since you can't tape it up. You can disable it, though, by plugging a converter or some other cord into the computer's microphone jack, which turns off the internal mic.

But ultimately, there's only so much you can do. Vulnerability is a fact of cyber life: Anytime you open a portal to the outside world, it makes intrusion possible. The problem is when we don't even know the portal exists, or are only dimly aware of it. There's a general rule that you shouldn't write anything in an e-mail that you wouldn't want shared with the world. Perhaps the same should apply to dancing in your underwear while your laptop is watching.

Correction, April 6, 2009: This article originally misspelled the name of Symantec Security Response. ( Return to the corrected sentence.)