Facebook keeps tabs on your username and password. It scans sites like PasteBin weekly to make sure hackers aren’t dumping people’s credentials. Another measure is stripping every user of their referral URL when they click one of the two trillion links posted to Facebook every day. Facebook also keeps a watchful eye on bad practices referred to as “likejacking” and “clickjacking.” If it suspects something is actually spam, it will give present you a pop up asking you if you really want to Like it before you actually hit the button.”]
Source: https://gizmodo.com/how-facebook-security-guards-your-info-5913408