Online advertising is crucial for advertisers. Due to its performance accountability and measurability, the cost-per-click (CPC) model has become the leading pricing model in online advertising and won nearly 60% market share. Since the advertising cost of the CPC model is directly related with the advertisement click volume, the CPC advertising is inherently vulnerable to click frauds. The click fraud occurs when the purpose of an advertisement click is to falsely increase the advertisement click volume rather than being interested about the relative advertisement. Currently, the click fraud problem is seriously jeopardizing the online advertising ecosystem. Synthesizing the game-theoretical analysis, the empirical data validation, the computational experiment and the statistical machine learning method, we study the incentive, characteristics, impacts and preventions of click frauds in this doctoral thesis. We also discuss impacts of market factors on the click fraud and the fraudulent click detection method. Our results shed light on the resistance and prevention of the click fraud problem. Main results and contributions of this doctoral thesis are summarized as follows. 1. Differently with previous works, which commonly consider publisher inflation frauds as exogenous factors, we model the publisher inflation fraud as an endogenous competitive strategy. Based on game-theoretical analyses on the publisher inflation fraud in the CPC advertising market, we have found that, a) the only publisher in the market won't commit frauds; b) when there exists competitions among publishers, committing frauds are publishers' equilibrium strategies; c) in the market equilibrium, publishers with different market shares will adopt different strategic fraud ratios; d) the publisher who is larger in the market share gains strictly lower payoff than the fraud-free scenario, while the smaller publisher may get a higher payoff than the fraud-free scenario in equilibrium. In addition, the total publisher payoff is reduced by click frauds, which harm the market efficiency. 2. By proposing a two stage game among advertisers, we analyze the advertiser competitive fraud. Our analysis results illustrate that, a) the existence of advertiser competitive frauds is impacted by advertiser budgets, the fraudster's value and the market fraud punishment level; b) the reserve price mechanism can effectively restrict advertiser frauds; c) the normal advertiser's return on investme...
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