The files show a wealth of information linked to online accounts, including GPS locations, file transfers, and chat logs, according to the database discovered by Victor Gevers, a security researcher at Dutch non-profit GDI Foundation.
The data collection appears indiscriminate -- some conversations are simply banter between teenagers, like one commenting on someone's weight and clothing size.
"They know exactly who, when, where and what," Gevers told AFP, explaining that thousands of records were piped daily to different databases for local law enforcement to review.
Government procurement documents and database records shared by Gevers show that the database is linked to an "internet cafe management system" developed by HeadBond.com, a tech firm based in eastern Shandong province.
In 2017, the public security bureau in Yancheng city, eastern Jiangsu province -- where at least one internet cafe named in the database is based -- contracted HeadBond for a system that monitors online activity at internet cafes.
On its website, the company calls its internet cafe management system "the best solution" for identifying online users for police on its website.