I would also like to know that.
There are a number of them. I think Acxiom is one of the bigger ones, and there are other examples. I think ChoicePoint has historically been an interesting one that was mining data from various sources and created profiles for law enforcement to use in the States.
There are a number of them out there of varying sizes, and that's part of the problem, in that it's hard to get a complete picture of where they all are and exactly how their data flows. Some of it is collected from the vast amounts of information that's now publicly available. In a social media context, I think that should be one of the factors we're taking into account when we're deciding where privacy defaults should be set, and those kinds of things.
As for another potential avenue for information to flow to these databases from sites like Facebook or others, though I don't want to single out any specific companies, there are a lot of third-party applications that get put onto Facebook, such as FarmVille and games like that.
I think it's actually a violation of Facebook's terms of use to sell information further downstream to these brokers, but it's not very clear exactly how that's enforced. I think technically Acxiom could make its own application and put it on Facebook.