How does "tiger woods adultery sale" bring you a dictionary page?

I just clicked away from a fluther page only to realize a second later that an ad on that page had been headlined “tiger woods adultery sale.” I thought “wtf?” and clicked Back, but it was no longer there. So I Googled on that expression: “tiger woods adultery sale”—thinking maybe some outfit really was capitalizing on that news story to promote a product (I was dying to know what product).

The Google search results looked like this.

What I want to know is this: how could someone (apparently) hijack sites like Dictionary.com, Thesaurus.com, and bizrate.com, all very popular sites, with their keywords and their Johnson & Murphy shoe ad? Is that what I’m seeing here—hijacking? How is this specific type of finagle done?