The big problem with this is you're giving the site access to loads of information about you. That's scary because the sites that use your credentials from Google, Facebook, LinkedIn, Twitter and other sites suddenly have access to your name, photos, email address and more information that you'd like to keep private.
We're all guilty of letting our guard down when it comes to privacy. It's understandable - who wants to type in pages of information about you to sign up for a new site when you can just let the site grab that information from Facebook?
Worse, you've probably signed up for dozens of sites this way over the years. The good news is, it's pretty easy to find out which sites are spying on you by checking your profile on Facebook, Google and other social media sites.
To find out which apps can access information about you on Facebook, you start with the menu. That's the down arrow to the right of your name on your Facebook news feed or timeline. (See red arrow below.)
Click on Settings >> click on Apps on the left-hand side of the page >> then click on specific apps to see what information they can see, like your email address and birthday. This is creepy. You might also see a note saying the app can post messages to Facebook on your behalf. This is what it says.
If you want to change the information that each app can use, click or un-click on the blue circle with a white check mark in it. When you don't want an app having access to your friends or email address, for instance, click on it.
The blue circle will be grayed-out when you turn it off. It's a bright blue when it's on.