Trespass to Chattels
Trespass to chattels is a tort whereby the infringing party has intentionally (or in Australia negligently) interfered with another person's lawful possession of a chattel. The interference can be any physical contact with the chattel in a quantifiable way, or any dispossession of the chattel (whether by taking it, destroying it, or barring the owner's access to it). As with all intentional torts, it is "actionable per se" so no proof of damage is required.
The origin of the concept comes from the original writ of trespass de bonis asportatis. As in most other forms of trespass, remedy can only be obtained once it is proven that there was direct interference regardless of damage being done, and the infringing party has failed to disprove either negligence or intent.
In some common law countries like the United States and Canada, a remedy for trespass to chattels can only be obtained if the direct interference was sufficiently substantial to amount to dispossession, or alternatively where there had been an injury proximately related to the chattel. (See Restatement (Second) of Torts, 1965.)
Damages from a trespass claim are limited to the actual harm sustained by the plaintiff (which can include economic loss consequent on the trespass - e.g. loss of profit on a damaged chattel). In cases of dispossession, the plaintiff is always entitled to damages if they can prove the dispossession occurred, even if no quantifiable harm can be proven.
Chattels are tangible personal property. Trespass to chattel is then primarily borrowing or utilizing chattels of another without permission. When I was in law school, this was one of those archaic torts that you have to learn about, but never expect to see, since damages are traditionally based on the actual harm done the owner of the chattel by the party trespassing thereof. Thus, if someone steals your bike, you can sue them, but if they don't harm the bike, you probably aren't going to get any damages. But a recent case, Sotelo v. DirectRevenue LLC, No. 05 C 2562 (ND Ill. Aug. 29, 2005), may have changed that.
In Sotelo, the plaintiff sued the defendant for installing spyware on his computer. One of his causes of action (or legal theories) was trespass to chattels. The defendant moved for summary judgement on this claim, and the Court denied. It found sufficient basis for such a claim to allow the case to go forward. Some comments on the case can be found in an article in USA Today by Eric Sinrod, Eric Goldman's Technology & Marketing Law Blog, and an article in freerepublic.com by Ernest_at_the_Beach. Goldman points out that:
The court explains a little more about what constitutes "causing harm" by noting that the plaintiffs allege that spyware:
1) causes significant and cumulative injury to computers
2) interferes with the computer usage
3) slows down the computer
4) uses bandwidth
5) increases "Internet use charges"
6) depletes a computer's memory
7) uses pixels/screen space on monitors [this one is pretty silly]
8) requires more energy because slowed computers must be on longer [also pretty silly]
9) reduces user productivity
10) increases user frustration
In the case of the Sony DRM root kit code, an argument can be made that ##1, 2, 3, 6, 8, 9, and 10 are potentially applicable.