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When I use Facebook, after I log out, I can see my profile picture on the login screen of Facebook. With great curiosity, I click on the profile picture (while I am still logged out) and Facebook logs me in again!

How can Facebook allow me to log in just via clicking on the profile picture on the login screen, without any password? What about library PCs and other shared computers? Isn't this extremely dangerous?

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  • I'm embarrassed to see that 10 months after this question was asked, there is no coverage here of how dangerous this approach is, especially since Facebook offers a popular single-sign-on feature as well. This flies in the face of the trend to "2 factor authentication". And now we know how Facebook exposed over 50 million people to security issues on not just the Facebook site itself, but countless other linked services. See The Facebook Security Meltdown Exposes Way More Sites Than Facebook | WIRED
    – nealmcb
    Oct 2, 2018 at 17:29

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This is a feature of Facebook to make logging in easier by not having to enter a password every time.

How does it work? Cookies.

Facebook uses cookies to identify you so that when you log out, you're able to login again without a password. This feature can be disabled as follows: Settings -> Security and login -> Login using your profile picture -> Turn off profile Picture login.

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    And when it's needed to be entered, you get locked automatically. 'Great' 'feature'.
    – Overmind
    Dec 4, 2017 at 10:34

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