In Social Networking site's like Facebook, Twitter, etc has many fetcher that's impotent for site's user to secure there information and save to be hacked like recovering password or hide your information .
If we talk about Facebook, so there are so many person who send unauthorized request to unknown person by searching someone's friend's list.The best solution for these problem is Hide your friend's list not only publicly as well as your's friend's because we don't know whom we trust.
To hide your friend's list in Facebook just Login to your Facebook Account and go to your profile by click at your profile image or simple hit on your image icon at right top
As shown in screenshot
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Then you will see your Facebook profile, look at the left bottom of your profile you will see your friend's list, click Edit family friend's and relationship as shown screenshot no 2, After this new window will open
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just set the permission on only me and you will don also you hide other information like your subscriber list or relationship status
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well that's it now save what you have been done ,view you profile by view as function enter some of your friends name and you will see your friend list is hidden .