Today’s release from fugitive NSA leaker Edward Snowden says that the NSA was spying on users through the cookies that web browsers save to customize commercial space on sites like Google.

According to an internal presentation slide showed that when companies follow internet consumers to better serve advertising it opens the door for government tracking. The slides suggest the NSA was already using the tracking to follow targets.

Online privacy advocates had been claiming for years the tracking tools called “cookies” left open the possibility for violations of web user privacy.

Cookies can allow the NSA to track a single individual’s communications among all internet transactions. Cookies are not just reserved for browsers on desktop or laptop computers. Smartphone apps that run on iPhones and Android devices, even the Apple and Google operating systems, track the location of each device sometimes without alerting the device’s owner.

The slides did not say how the NSA obtained access to Google’s tracking system.