The Safari browser even goes one step further. It also deletes certain first-party cookies after 7 days. This already has consequences for your Google Analytics data. For about 33% of your visitors, the returning visitors can only be recognized within a week. 2. Ad blockers stay Ad blockers are not new. Its use is slowly growing: 34% of the Dutch now use an adblocker. Some of them protect a large number of cookies by default. For this article, I did a little experiment with four common ad blockers.