Correct me if I'm wrong, but I think it is fairly easy to detect the noise generated by this kind of tools and retrieve the real history, for example: users can generate a bunch of fake entries in their browsing history but if at the same hour every day they visit the same websites, well, that is some regularity that can be exploited.<p>Anyway, history can be sold even with noise, in this case users will see mostly ads about products in which they are not interested in, which could be, I think, much more annoying.