These apps often serve as fronts for malware, data harvesting, or credential theft.

You can see exactly who viewed your 24-hour stories.

: If a profile is set to "Public," you can often view its basic information (name, profile picture, and public posts) through a browser without logging in. You can simply copy the profile URL and paste it into an incognito or private browsing window.

The most common "viewer" is a simple HTML form. You paste the profile URL you want to view anonymously. It asks you to "log in with Facebook to verify you aren't a bot." You enter your email and password. Congratulations: you have just handed your Facebook credentials to a hacker in Russia or Nigeria. Within minutes, they will change your password, lock you out, and use your account to scam your friends list.

Emily was skeptical at first, but her curiosity got the better of her. She clicked on the link and was directed to a simple webpage with a text box asking for the Facebook profile URL she wanted to view. Emily entered the URL and clicked on the "View Profile" button.