The number of potential free-riders is tiny, so there's no reason to retaliate against them. The same problem exists in Internet services. If blekko (a startup

The number of potential free-riders is tiny, so there's no reason to retaliate against them. The same problem exists in Internet services. If blekko (a startup search engine) saw a DNT do not track header from a user, we wouldn't even include their queries in our anonymized dataset. That slowed our learning-to-rank process, but only by a little.