# Real-Time Filtering Non-Intentional Bid Request on Demand-Side Platform
## 2 Online Advertising and Real-Time Bidding
### Advertising Fraud in Regard to Ad Exchange  
Advertising fraud is a principal concern for all marketers. Advertising fraud is any attempt to defraud advertising platforms for the purpose of financial gain. In particular, it is the practice of fraud in impressions, clicks, conversion, or data events and this will affect both advertisers and publishers from the ad exchange's perspective. There are different methods by which fraudsters can carry out advertising fraud. The following are several common types of advertising fraud:  
* Botnet advertising fraud: causes a huge number of fake clicks, fake visits to websites, and fake traffics [4]. Botnet is an interconnected network of users' machines which are installed with malicious software or pieces of coding to perform automated tasks and execute fraud actions;
* Click hijacking: thieves click by redirecting a click on one ad to an irregular ad. To execute a click hijacking attack, fraudsters will intrude a user's device, website, or proxy server;
* Click spamming, click injection: a form of mobile advertising fraud which automatically generates a large number of fake clicks or impressions to steal an advertiser's budget [4];
* Ad stacking: one type of impression fraud with programmatic ad placements. In order to execute this attack, a fraudster stacks layers of multiple ads on top of each other to hide illegitimate ads under legitimate ads. In this way, the illegitimate ad also gains impressions, even though it is hidden behind another ad [5];
* Ad injection: illegitimate ads that insert into legitimate ad space on a website without their permission via malicious browser extensions or malware. In this way, an illegitimate ad can replace the existing ad entirely or display itself on websites that are not supposed to contain ads.  
### Advertising Fraud in Regard to Ad Exchange  
Advertising fraud has been hurting online advertising at various levels. It is essential to have countermeasures to detect and prevent these kinds of frauds. Due to various forms of advertising fraud, various methods are used to deal with ad fraud in the context of an ad exchange [5].  
* Statistical-based anomaly detection: analyzes a large-sized bid request dataset and creates an algorithm to detect abnormal activity. This type of detection is used to identify fake traffic;
* Anomaly-based detection: observes the unexpected increases in the number of impressions and CTR of the publisher by using the publisher's history. This detection can be used to recognize unusual publishers [6];  
Figure 1: Real-Time Bidding Process.  
Signature-based detection: a process by which static rules are defined to decide whether ad traffic should be considered abnormal or not. These static rules are conducted by looking for characteristics within a large amount of ad traffic to identify malicious behaviors. Signature-based detection is only useful in recognizing attacks that are already known; however, it cannot identify unknown attacks [6];
* Website popularity and page ranking: checks the reliability of websites by comparing their actual amount of traffic and the suggested page ranking. There are some ranking websites such as Alexa or Compete [6].