Online banner advertising began in the early 1990s as page owners sought additional revenue streams to support their content. Commercial online service Prodigy displayed banners at the bottom of the screen to promote Sears products. The first clickable web ad was sold by Global Network Navigator in 1993 to a Silicon Valley law firm. In 1994, web banner advertising became mainstream when Hotwired, the online component of Wired Magazine, sold banner ads to AT&T and other companies. The first AT&T ad on Hotwired had a 44% click-through rate, and instead of directing clickers to AT&T’s website, the ad linked to an online tour of seven of the world’s most acclaimed art museums.
GoTo.com (renamed Overture in 2001, and acquired by Yahoo! in 2003) created the first search advertising keyword auction in 1998. Google launched its “Ad Words” search advertising program in 2000 and introduced quality-based ranking allocation in 2002, which sorts search advertisements by a combination of bid price and searchers’ likeliness to click on the ads