A few months back on Kairosnews, we had a long discussion with Michael Bruton, a representative of Turnitin, a commercial "plagiarism detection and prevention service." In short, the question was whether it was ethical for teachers to use the service, since it involves uploading students' essays into turnitin.com's database, where they will ostensibly be encrypted and then used to guard against their being used illicitly in the future. Students at various schools across the country have protested the software as well, arguing that (a) the service is very expensive, and student's don't want to pay for it, and (b) they feel it violates their "intellectual property rights."
Obviously, there is quite a cloud of confusion here regarding all sorts of issues and rights. Most obviously (to us, at any rate), Turnitin.com is non-free software, and it's very expensive (upwards of $50-75,000). Furthermore, it assumes the conventional "intellectual property model" that insists that intellectual work, in this case student essays, ought to be treated as "property." Even still, whose "property" is it? Even if we accepted the metaphor, it's unclear how submitting a student's paper (usually under coercion) to a for-profit company is an ethical use of someone's "property." We'd be much harder pressed, for instance, to force a student to remove his tennis shoes and submit them to a machine to prove they weren't stolen. There are all kinds of policies and laws regulating that type of behavior...
On the other hand, I've heard the argument that this service isn't so much about catching cheaters as teaching proper attribution. Teaching students how to cite their sources is an important part of any writing class, and I see how this can transfer even to programming. It wouldn't be ethical (and is, in fact, illegal) for coders to "copy and paste" GNU-licensed code into their closed-source projects and then sell it, all without acknowledging where they got their code. So, shouldn't it be the same for essays? I suppose we can assume that there do exist students who simply aren't aware of the rules of attribution (that is, they aren't intentionally doing something wrong).
It's a thorny issue, and I've discussed it with plenty of other writing professors, but I'm interested to hear from another perspective. Would a service like this be wrong if it were conducted with free software? Or is the whole idea off-base?