Low-level security features
Turn off auto-login: Auto-login lets your Mac start up without a password—it automatically logs in the person who has “auto-login” turned on in the Accounts preferences (click “Login Options” at the bottom of the list of accounts).
Then be sure to log out before you leave your computer for a while. This ensures that people walking by will need a password to log back in to your account, even if they restart your Mac. Laptops should always require a login password.
If you don't want to turn off auto-login, you might want to take the extra step to uncheck the box to “Show the Restart, Sleep, and Shut Down buttons.” Because ...
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