Popular social media platforms and video streaming services pose serious risks to user privacy, with children and teenagers most at risk, the Federal Trade Commission found in a report published Thursday.

The FTC just published results of a sweeping study of social media sites that has been going on for four years. The organization said that many social media sites and streaming services engage in “vast surveillance of consumers in order to monetize their personal information.

The report by the Federal Trade Commission claims social media and video platforms collect troves of personal information from activity across the internet for use in targeted advertising.