First of all, the monitoring starts the first time the user visits Facebook, by creating a browser cookie, while in case of registration you also create a session cookie.
After the first "contact", every time the user visits any website that has a Facebook plug-in (eg Like, Share buttons, Facebook Connect, etc.), the cookie informs Facebook about the name of the website and the time of the visit.
This information includes the IP address, the browser used, the operating system, screen resolution, etc., and Facebook keeps a 90-day file, automatically deleting older entries as new ones arrive.
Facebook has the ability to track the user's movements even when it is not connected to the social network, which has caused a great deal of controversy, but Bejar states categorically that this is against the company's policy and of course does not apply.
After all, as Mark Zuckerberg recently stated, the practice of tracking users is typical of any online ad-related network, including Google, Microsoft, and Yahoo.
As you can see, the movements of each of us on the Internet play a role in creating trends (even if we do not want to) and become a golden tool for advertising companies. Source: Techgear.gr