## 7 Fraud in Ad Ecosystem
### Categories of Ad Fraud
#### 7.1.3 Action Fraud  
Action Fraud occurs when a fraudster falsifies a user's action in order to generate revenue for himself. Examples of such actions are filling an online form, placing online purchases, signing up, registering, or downloading an item corresponding to an ad. This type of fraud exists in several different forms, including conversion fraud, re-targeting fraud, affiliate fraud. 1. Conversion Fraud: Conversion is any interaction with an advertisement that ultimately generates value (e.g., online purchase). Consequently, conversion fraud occurs when a conversion is artificially generated by a non-human entity (e.g., a bot) or by a human with malicious intent. Typically, upon a click on an advertisement, the user is redirected to the branding site (or landing page), which shows summarized information about the advertised services or product. For any purchase through such a landing page, the user  
Figure 5: An illustration of click inflation attack involving a fraudulent publisher publisher.com, a fraudulent website example.com, an advertiser advertiser.com, and a user. (1) The user clicks on (i.e., retrieves) example.html which contains a script code that silently redirect the user to publisher.com. (2) The user gets redirected to publisher.com which keeps two versions of webpages: a valid/original and a manipulated version. (3) publisher.com presents the manipulated page to the user if the referrer field in the HTTP request points to example.com. (4) publisher.com triggers/generates a click on its ads without the user’s knowledge. Otherwise, publisher.com will direct the user to the valid webpage and allow him/her to decide whether or not to click on the ads [4]. is typically required to fill out a form by providing personal information such as name, address, and credit card number. One way of conducting conversion fraud is by filling these forms with fake or stolen customer information. Conversion fraud is generally committed either utilizing lead bots or by lead farms. Lead bots are automated computer programs that can fill out thousands of forms in a blink of an eye with either random or correct information. They are also able to click a link or download files automatically. On the other hand, in the lead farm method, genuine human labourers manually perform clicks to conversion with a malicious intent [1]. 2. Re-targeting Fraud: Identification and targeting of valuable customers based on their previous online behaviour patterns are common practices in ad-serving platforms. This process is also known as re-targeting [56] or re-marketing. As mentioned earlier, different tracking techniques (e.g., use of cookies) can be deployed to facilitate user re-targeting. The fundamental goal of re-targeting fraud is to give a false impression about previous customers' behaviour and pretend they have an actual interest in a specific product or a service. In other words, through re-targeting fraud, fraudsters attempt to mislead advertisers into believing that fake users (e.g., a group of bots) are prospective purchasers and encourage them to put a higher bid price on impressions generated by these bots. 3. Affiliate Fraud: In affiliate marketing [57], a business entity (also called an affiliate) is rewarded for every visitor that is ultimately brought to the advertiser's site. Affiliate fraud encompasses a range of fraudulent activities that aim to fool the ad system into giving revenue to an affiliate while he/she actually does not qualify for it. Malware or Adware, cookie stuffing, and URL hijacking methods are three types of affiliate fraud. Malware or Adware (an unwanted software designed to generate advertisements on the screens [58]) installed in a user's device can redirect him/her to the advertiser's site via a fake affiliate marketing link. As a result, the affiliate can be in the position to claim a commission from the advertiser.