From Ynet News, with thanks to Alain:
Terror organizations are advancing their recruitment and public relations methods: Internet surfers who enter the word “Hamas” in Arabic in the Google search engine, will view, in addition to the search results, an AdWord message that links directly to the website of the organization’s military faction Izz al-Din al-Qassam Brigades.
The link also appears in a search of several other words, such as the “Gaza,” “Palestine,” “Jihad.”
This indicates that a Hamas source has paid Google, the most popular search engine on the web, for the advertisement.