Much advertising on the Internet operates on a "pay-per-clickâ€ model, in which the operator of a website that contains advertisements receives a fee from the advertiser every time a visitor clicks on the ad. Criminals sometimes use botnets to generate fraudulent "clicksâ€ on pay-per-click advertisements. For example, a bot-herder may set up a website with advertisements and negotiate an arrangement with a web host that pays the bot herder for clicks on their ads. The bot-herder then writes bot code that automates the click-throughs so that the bots in the botnet, which can number in the thousands, instantly click on the ads on that website. The pay-per-click marketer, honoring the advertisement agreement, pays for these illegitimate clicks without gaining the sales or leads that were hoped for. This process can be further enhanced if the bot hijacks the start page of a compromised computer so that the click-throughs are executed each time the owner of the compromised computer opens their browser, victimizing both the owner of the compromised system and the web host.