Yes, That Website You’re Visiting Is Probably Tracking You by Sy Mukherjee @FortuneMagazine August 17, 2016, 8:17 PM EST E-mail Tweet Facebook Linkedin Share icons If you’re on one of the most popular sites on the web, you are almost certainly being tracked. That’s according to a new study published by University of Washington researchers, who found that at least three-quarters of the world’s most visited sites use web tracking tools. The authors used the Internet archive Wayback Machine to trace various sites’ source codes over the years to check for tracking software, according to USA Today, and discovered that the percentage of the world’s 500 most popular websites with web tracking code ballooned from 5% to 75% between 1998 and now. And at least half of those sites have four third-party trackers. Google’s goog DoubleClick ad server system was the most common system, found in 15% of sites. Third-party tracking has exploded in the era of digital commerce as companies scuffle to figure out exactly what types of products and services a user may be interested in so they can better target advertisements to them. Tech giant Facebook fb , which recently reported a substantial spike in ad sales, has even announced plans to entice advertisers in emerging markets. Last week, it said it was trying to stop ad blockers from working the site, prompting a rebuke from the popular AdBlock Plus service.