Privacy is already gone.

—Larry Ellison, CEO, Oracle Corp.

ILLUSTRATION: BRIAN STAUFFER

In his 2005 book, The Traveler: A Novel, John Twelve Hawks describes a near-future world in which almost everything we do is traceable and almost everywhere we go is trackable. Using high-tech tools such as Echelon (the global spy network that monitors electronic communication), the Global Positioning System, RFID tags, centralized databases, tracking software for credit card charges, and surveillance cameras with facial recognition software, the "Vast Machine" can watch anyone, except those few who elect to live "off the Grid."

It's a paranoid book, but, as they say, being paranoid doesn't mean someone isn't out to get you. In reality, surveillance is growing at an alarming rate, and so, too, are the words and phrases we need to use to keep up.

Did you know, for example, that you cast a data shadow? This is the trackable data that you create by using technologies such as your credit cards, cellphone, and the Internet. This is also sometimes called the paperless trail, the electronic equivalent of a "paper trail." A similar idea is the pseudonymous profile, a collection of data associated, usually, with the IP address of a user's computer. The profile describes the user's online activities, interests, and habits, so a Web site can personalize pages or, more often, target advertising at that IP address.

Some even envision a world of anticipatory surveillance, where the data collected enables the site (or whatever) to anticipate a person's actions or needs. (The opposite is preemptive surveillance, which tracks behavior in order to prevent people from doing something they shouldn't.) This is a low-end variation of a digital silhouette, a profile generated by a software program that monitors a user's surfing habits.

The data for this profile comes from users who agree to install the software in exchange for a cheap computer or cut-rate Internet access. Because the user agrees up front to be monitored, this kind of program is called opt-in surveillance or voluntary surveillance. The opposite would be a data spill, an accidental transmission or display of private online data to a third party. It's the online analogue to an oil spill, the leakage of petroleum from an oil tanker or other vessel. Whatever the source, we are therefore increasingly susceptible to dataveillance, the ability to monitor people's activities by studying their data shadows. A synonym that isn't as popular, but rolls off the tongue a little better, is consumer espionage.

We like to think that all this surveillance is part of some dastardly plot cooked up by those twin pillars of the modern Big Brother: Big Government and Big Business. Unfortunately, surveillance is all too common among us little folk, too. A common example is the nanny cam, a special video camera—small enough to be concealed inside stereo equipment or a teddy bear—used for spying on babysitters. A similar idea is the kiddie cam, a camcorder that displays a live feed so that parents can monitor either their children or their children's babysitter from a remote location. Kiddie cams are also known as kinder cams or cradle cams.

Even creepier are the great lengths some husbands and wives are taking to detect Internet infidelity, an online romance or affair conducted by their spouses. Web sites such as http://www.chatcheaters.com and http://www.infidelitycheck.org offer not just advice on dealing with an Internet cheater but also sophisticated electronic tools. For example, you can purchase a keylogger, a program or device that records a computer's keystrokes. (A subset of the genre is the chat logger or IM logger, a utility specifically designed to record chat conversations held in instant messaging environments, such as AOL, MSN, and Yahoo.)

Think your lesser half is cheating via the home computer while you're at work? No problem. Just install remote monitoring software, which tracks everything that happens on a computer and sends the results to a remote location (such as your work e-mail account).

Are we becoming what sociology professor David Lyon at Queen's University, in Kingston, Ont., Canada, has called the surveillance society? Is there hope for privacy? Larry Ellison might not think so, but an increasing number of people are fighting back by using a technique called sousveillance (or sometimes inverse surveillance). University of Toronto electrical and computer engineering professor Steve Mann calls it "watchful vigilance from underneath." (The "sous" in sousveillance is French for "under"; the "sur" in surveillance is French for "over.")

It's a kind of countersurveillance where people take pictures of surveillance cameras or record people in positions of power or authority and then post those pictures or recordings on the Web. Think of it as the watched watching the watchers, and that can only be a good thing. If you think so, too, be sure to celebrate World Sousveillance Day on 24 December.