Trespass you understand; chattels is just property, as opposed to land, and just as you can trespass on someone's land, you can trespass their movable stuff, or chattels. If you deprive the owner of his stuff, or the use of it, or damage it, and the owner didn't give you permission to use the stuff, you could be looking at a trespass to chattels claim.

It started with cases involving things like taking a man's horse for a ride, without the owner's permission. There have been a string of cases applying trespass to chattels to computers, and the main difference is that in a computer context, you usually have to prove some damage, whereas with land, it can be enough just to put your foot on my property, if I have a No Trespassing sign up, even if you don't steal apples off my tree.

In this case, the plaintiff is alleging the following as damage sustained from adware: wasted time, computer security breaches, lost productivity, and additional burdens on the computer’s memory and display capabilities. The lawyer handling the case says that the next step will be to ask the Court to permit the claims of "hundreds of thousands of computer users to be heard in a single lawsuit (i.e. a 'class action')."

Note what Eric Sinrod, an attorney with the firm of Duane Morris, concludes in his Cyberspeak column for USAToday, "Spyware can constitute illegal trespass on home computers":

A federal trial court in Chicago has ruled recently that the ancient legal doctrine of trespass to chattels (meaning trespass to personal property) applies to the interference caused to home computers by spyware. . . .

The lesson here is that companies and individuals must be mindful that even though specific laws may not yet be on the books with respect to new types of online conduct, traditional legal principles may be applied by the courts, with potentially significant consequences. Prudence suggests that attorneys who are expert on Internet issues should be consulted when a company or an individual is not sure that certain behavior on the Web potentially could create liability.

He's saying that just because there is no apparent law specifically forbidding certain activity on the Internet, it doesn't mean a judge can't dig up an old law and use it against someone who causes harm to others.

The FTC has recently brought a case against adware too, which you can read about here. In the complaint [PDF], in FTC v. Odysseus Marketing, Inc. and Walter Rines, you'll notice that on page 3 it says that the adware interferes with normal Internet use and degrades computer performance. They explain on page 5 that the adware also interferes with search results when users search on Google or Yahoo, providing fake results. That has to be annoying.

Of course, if you use GNU/Linux systems, you don't have these problems. If you wish to escape such issues, do consider at least changing your browser, if not your operating system.

Here is another trespass to chattels case, a New York case, Michaeli v. eXact Advertising, also against an adware company. My point is that trespass to chattels is being used all over the place.

Here is some commentary on the Sotelo v. DirectRevenue case by Eric Goldman, who teaches "cyberlaw, intellectual property, copyrights, contracts, software licensing and orofessional responsibility" at Marquette University Law School, and who clearly isn't so pleased with the Sotelo v. DirectRevenue ruling, for reasons also amplified in this editorial.

You can probably figure it out from the allegations. For example, in the class action case Michaeli v. eXact Advertising, the complaint begins like this:

The Defendant, eXact Advertising, LLC ("eXact Advertising") has unlawfully used and damaged Plaintiff's rights to use and enjoy his personal property. Without Plaintiff's authorization, eXact Advertising infected Plaintiff's computer with harmful and offensive spyware programs by deceptively bundling its malicious software with a wide variety of "free" games, cursors, screensavers and other small software programs. These harmful programs would then secretly track Plaintiff's Internet use, thereby invading his privacy and damaging his computer. Utilizing this software, eXact Advertising would monitor the Internet "surfing" and/or web-browsing activities of the Plaintiff, ultimately bombarding Plaintiff's computer with intrusive advertisements ("adware"). In addition to invading Plaintiff's privacy, eXact Advertising's unwanted spyware and adware programs illicitly caused Plaintiff's computer to slow down, consume excessive bandwidth over Plaintiff's Internet connection, monopolize computer resources, including memory, pixels and monitor screen-space, and disable or destroy user-installed computer software, ultimately causing many computers to crash.

You'll note that paragraph 14 explains that the offending adware, Bargain Buddy, is "an Internet Explorer browser helper that is designed to run at startup and constantly monitor a user's internet browsing through the web pages requested and the terms entered into the browser." When there is a match, a popup ad is shown. If the user clicks on the ad, revenue goes to eXact Advertising for directing traffic to the advertiser's website. The case involves other spyware too, and it all tracks the user's activities and reports back to eXact, according to the allegation, and without appropriately asking for users' consent before installing the spyware.

As a result, the complaint alleges, spyware "causes computers to slow down, take up bandwidth, use up memory, utilize pixels and screen space on monitors, and frustrate computer users." Their productivity is decreased, because spyware requires hours and money spent to try to figure out how to uninstall the stuff, as well as closing ads, and users have to run their computers longer, because they are slower, and so use more electricity, decrease the life of the computer, and cause increased Internet access charges.

You may be saying, some of the things on the list sound a bit silly, like using pixels on the monitor, but the list is to establish that the spyware is using the user's computer, without authorization, and in such a way that the user is prevented from using it fully himself. That is what you need to prove to establish a trespass to chattels claim. If I take a little spin in your car, without your permission, even if I don't harm it, it's trespass to chattels. Why? Because it's your car, your property (chattels) and I don't have your permission to drive it (trespass). Even if I don't harm your car and even top off the gas before I bring it back, it's still trespass to chattels. Ditto here, and in paragraphs 46 and 47, they provide the computer equivalent to my joy ride in your convertible:

46. In doing so, Defendant has intentionally intermeddled with, damaged, and deprived Plaintiff of his computer and/or Internet connections, or a portion thereof, without authorization.

47. Defendant, without authorization, intentionally through the use of a computer or computer network, used Plaintiff's computer in such a manner and extent as to exercise dominion over such property or, in the alternative, in such a manner and extent as to deprive Plaintiff of his use and enjoyment of this property thereby in each instance trespassing on Plaintiff's property for its own commercial use.

Even if I don't harm your car, you don't get to drive it while I'm joyriding. Ditto with computer interference, or so goes the theory. The ruling cites a number of famous trespass to chattels cases, which you can find here along with some explanation. Here's my favorite explanation of trespass to chattels, "The Trouble with Trespass," by Dan L. Burk. It explains what it is in the first paragraph:

Trespass to chattels is a somewhat obscure tort action arising out of unauthorized dispossession, use, or interference with the tangible property of another. Under the Restatement formulation, the trespass action requires some intentional physical contact with the chattel. Unlike its cousin, trespass to land, trespass to chattel requires some substantial interference with the chattel, such as removal, damage, or similar impairment of its physical condition. Trivial interferences never constitute a dispossession, but the harm necessary to trigger liability may arise from an injury to someone or something other than the chattel itself, so long as the harm bears a proximate relationship to the dispossession.