We all know that our online presence is constantly being monitored and categorized by advertisers, and that our data is utilized to tailor marketing content to our specific needs and interests. However, a recent leak from Microsoft’s ad platform, Xandr, provides an unprecedented look into the staggering breadth and depth of this categorization process.

The leaked information exposed a database of 650,000 “audience segments” – detailed categories used by advertisers to target potential consumers based on highly specific, sometimes sensitive personal information. The range of these audience segments extends from commonplace categories like “Affluent Millennials” to more intimate, peculiar classifications such as “heavy purchasers” of pregnancy tests, those with an interest in brain tumors, and even individuals prone to feelings of being “easily deflated” or that they “get a raw deal out of life.”

This peek into Xandr’s audience segmentation is illuminating. It provides consumers with a rare opportunity to understand how advertisers perceive, categorize, and target them. More importantly, it shows how digital ad companies pool and amalgamate personal data, collected both from our online activities and real-world movements, to create bespoke, targeted groups of potential consumers.

According to Wolfie Christl, a privacy researcher at Cracked Labs who discovered the file and subsequently shared it with The Markup, this data represents the largest piece of evidence showcasing what he terms the “distributed surveillance economy.”

The Xandr leak has also raised concerns among privacy advocates and consumers alike. The potential sensitivity and intimate nature of some of these audience segments pose pressing questions about privacy, data protection, and ethical advertising practices. For instance, several categories pertain to health and reproductive issues, mental health conditions, and religious practices – topics considered private and sensitive by many.

Despite being contacted about the leak, Microsoft has removed the file from its website without further comment. What remains is an extensive array of questions about data privacy, consumer rights, and the lengths advertisers will go to in their quest for the perfect target audience. The debate on digital privacy and targeted advertising is far from over, and this incident serves as a stark reminder of the challenges we face in the era of Big Data.