Facebook, embattled in a scandal over the mishandling of user data, confirmed on Monday that it also collected information from people beyond their social network use.
During heated hearings in Congress last week, CEO Mark Zuckerberg had already explained that Facebook collects data beyond what users share on their profiles.
"When you visit a site or app that uses our services, we receive information even if you're logged out or don't have a Facebook account," product management director David Baser said in a post on the social network's blog.
"This is because other apps and sites don't know who is using Facebook," he added, noting Facebook was also following up with Congress on a few dozen questions Zuckerberg was unable to answer at the time of the hearings.
Baser said "many" websites and apps use Facebook services to target content and ads, including via the social network's Like and Share buttons, when people use their Facebook account to log into another website or app, and Facebook ads and measurement tools.