The advertising industry is simultaneously everywhere and incredibly difficult to investigate. Ads can power all sorts of surveillance, from the relatively mundane like inferring someone’s age or gender, right up to harvesting their precise location data and selling this to the government. But researching that omnipresent surveillance is, ironically, an uphill struggle because the relevant data is spread across the web, nestled in obscure files that most people never look at or even know to look for, and can’t be searched all at once.A new research tool called DecryptAds hopes to change that by bringing together a massive corpus of data. It can show what advertising brokers are operating on a particular website, and, more importantly, many other places those same brokers are operating. The tool cuts down on work that would ordinarily take much longer, and creates entirely new ways to explore the world of advertising and surveillance.💡Do you work for a data broker or advertising company selling this sort of data? I would love to hear from you. Using a non-work device, you can message me securely on Signal at joseph.404 or send me an email at joseph@404media.co.“For years I’ve personally worked on some of the biggest data privacy problems that have impacted the world, and I’m damn sick of people trying to guess how hundreds of data brokers are selling location data on people and a wide variety of other sensitive audience segments,” Zach Edwards, chief product and research at DecryptAds, told 404 Media. “We want to make it easy for anyone to look up a website or app and quickly understand the data sharing implications to risky ad tech companies and data brokers.” In a process called real-time bidding (RTB), advertising companies outbid one another to have their clients’ ads placed in the web browsing session or app of a particular type of person. A side effect of that process is that companies can harvest all sorts of sensitive information about peoples’ devices, in some cases including their location. 404 Media has covered this type of surveillance extensively, from an Israeli spy firm monitoring billions to uncovering thousands of specific apps that siphon location data, with middlemen then selling it to the U.S. government.When 404 Media and other outlets have investigated this industry, it has typically been through sources, leaks and hacks, or technical analysis of certain apps. DecryptAds takes a different approach. The site brings together ads.txt and app-ads.txt files — which list the advertising systems plugged into websites or apps — and sellers.json files which advertising exchanges use to list the companies they work with. Ordinarily these files cannot be easily compared to one another or searched in aggregate. DecryptAds makes that possible.