Gator sell those pop-up ads to advertisers who want to reach people who visit certain websites but without paying the fees that the owners of those websites would charge. For example, with Gator adware on their computers, people visiting the Hertz websites may be greeted by pop-up ads for rival car-rental companies. In an ad campaign for an automaker, Gator recently searched its database and found 1.3 million computers whose users had clicked through automotive websites to look at certain types of vehicles. Its then sent ads to those computers, varying the message depending on whether the pattern of web visits suggested the person was close to making a purchase or was looking at competitors, cars.