Search engine Google has made the biggest deal in their history, outbidding Microsoft to pay $3.1 billion for web ad supplier DoubleClick. Until now, Google's advertising business has focused on small advertisers, but DoubleClick's relationships with big online ad agencies and publishers will bring much bigger advertisers to Google such as MTV Networks, the magazine Sports Illustrated, and the Friendster social networking site. While some estimated two weeks ago that DoubleClick would sell for $2 billion, Google may have paid extra in order to prevent Microsoft from acquiring the company. The biggest winners are San Francisco private equity firm Hellman and Friedman, who paid $335 million for DoubleClick in 2005.