The mystery of how intrusive YouTube ads are evading ad blockers

The mystery of how intrusive YouTube ads are evading ad blockers

Browsers, Ad filtering, Uwe Bernitt, 10. June 2021

The last few weeks have put the online community on alert, as user experience has been challenged by YouTube, who made some changes to their platform that have rendered it impossible to block intrusive ads. This is the most recent example of the complexities of ad filtering and ad blocking and proof of how the 24/7 dedication and high-level expertise of our eyeo anti-circumvention* team are supporting our efforts to ensure a healthy user experience.

How it started

This mystery started a few weeks ago when the number of YouTube issue reports began steadily increasing. In fact, by mid-May, the reported issues were 10 times as high as at the beginning of the month. Many users complained that their ad blocker was no longer blocking intrusive YouTube ads.

To add to this mystery, many of our partners who are using our ad-filtering SDKs also started to complain, as their users were having the same issue and had given them the same type of feedback. In the meantime this had become so pervasive that the entire ad-blocking community had started to discuss the matter, puzzling folks from EasyList, AdBlock, uBO and others on Github and Reddit.

So what happened?

YouTube was able to evade all the blockers. But how? It appeared that YouTube started to do A/B testing. One assumption was that they made some changes to their technology which happened to cause ad blockers to not work as expected (without this being the end goal). Another assumption was that YouTube was doing this to bypass ad blockers on purpose.

Our dedicated anti-circumvention (anti-cv) team went into action. The anti-cv team’s main mission is to prevent these circumvention or bypassing efforts and keep the ad-filtering technology working effectively for its users. They thoroughly scoured the internet and researched everything there was on this issue. They reviewed hundreds and thousands of user-reported issues but still could not reproduce the issue internally. Platforms bypassing ad blockers is not something new, and we work on this every day, but not being able to reproduce it internally is what makes it so challenging.

How did we fix something we could not reproduce?

Since we couldn’t replicate the issue on our end, we had to start with a theory: one of what we call “snippet filters” from the anti-cv filter list we use (specifically for going against ad-blocking and ad-filtering circumvention) stopped working under yet unknown circumstances. Like any good detective, we had to test our theory. So we disabled existing filters and attempted to block the ads from scratch.

YouTube is the second-most-visited website worldwide, only behind Google. So this is where it gets pretty tricky. Millions upon millions of requests come in and when requests are very similar (which at that volume, they are bound to be), it becomes extremely difficult to find a part of the requests' addresses that differentiates content-related requests from ad-related ones. We tediously combed through parameters in the URLs, one by one, and tried it to see which one to target without breaking anything else.

On May 18th, only days after the issue was first discovered, we pushed a seemingly simple blocking filter, which, by nature, performs more effectively than snippets, and now the problem seems to be fixed for many users. But we're still keeping a close eye on issue reports for confirmation and to see if we should further improve upon the solution.

Current status - desktop issues were fixed and mobile is on the way

We may not have figured out why the ad blockers stopped blocking ads on YouTube in the first place but we have figured out HOW to start blocking them again. The fix is now available for Adblock Plus and Adblock users, as well as for our partners’ users who are consuming our anti-cv list.

Users who had the issue might notice longer loading times before the content video starts, sometimes followed by a white overlay with a "Skip Ads" button. We can easily "hide" this, but are waiting for user feedback to determine the best option. There’s already a significant and steady decline in issue reports, but out of an abundance of caution, we are continuing to monitor the feedback from users and the community very closely.

User experience is paramount to us and, while we are happy to have reacted so quickly and to have minimized the problem, we are not satisfied with the status quo, and are continuing to look for an even better alternative, while also considering all the incoming feedback to constantly improve our solution.

What about mobile? What’s next?

This is all very recent, and the battle is taking place in real time, however, we are hard at work on this, and we expect to have a solution that will satisfy our users and the users of our partners very soon.

In the future we will act just as swiftly and thoroughly to address any new mysterious issues as they arise. The current ad-blocking and ad-filtering circumvention challenges should not be underestimated and should be monitored and acted upon in a timely manner, so that the free internet can stay accessible for everyone. We are very grateful for all the feedback we have received from the user community and from our partners, which has allowed us to respond quickly.

* The practice of ad-filtering circumvention is when some websites use certain techniques to bypass ad-filtering software. The methods used are highly complex, requiring a considerable level of expertise to beat them. Therefore, we have a dedicated anti-circumvention team, who continuously monitors and works together with publishers to find the best solution to balance monetization and user experience needs. We take these steps because circumvention is detrimental to the building of a sustainable online ecosystem, as it means any rules around responsible advertising and allowlisting can be ignored.

Photo by Katie Rae on Unsplash