More and Scammier Ads: The Perils of YouTube's Ad Privacy Settings

When users disable online ad personalization, they might be anticipating to see fewer ads that are "relevant" to them as a trade-off for more privacy. In this paper, we show that the tradeoff can go much further than this intuition. We conducted controlled experiments on YouTube in Australia, Canada, Ireland, the United Kingdom, and the United States to investigate the impact of disabling ad personalization on the quantity and quality of ads that users receive. Through experiments where emulated users with different ad privacy settings watched sequences of 400 videos, we show that disabling ad personalization can lead to the user being shown as much as 1.30 times more pre-roll ads than the default (least private) setting. More concerning is that in our experiments, the proportion of predatory ads increased 2.69 times compared to the default setting, from 2.5% to 8.7% of ads. This result highlights that certain user demographics (in this case, privacy-conscious users) can be exposed to significantly higher rates of predatory ads, and suggests that the platform's efforts to curb such ads are still falling short.