Ad blockers, the digital shields that nearly one billion internet users deploy to protect themselves from intrusive advertising, may be inadvertently exposing their users to more problematic content, according to a new study from NYU Tandon School of Engineering.

The study, which analyzed over 1,200 advertisements across the United States and Germany, found that users of Adblock Plus’s “Acceptable Ads” feature encountered 13.6% more problematic advertisements compared to users browsing without any ad blocking software. The finding challenges the widely held belief that such privacy tools uniformly improve the online experience.