It’s not just Facebook: you can use your account with Google, Twitter, or other accounts to log in to many unrelated services. Using services like Facebook to provide authentication is a popular trend. Using the same account everywhere is even less secure than using the same password everywhere.
Facebook gets information about every service where you use Log in with Facebook.The service does not get your Facebook password.If you must use it, make sure your Facebook account is secured.Using a unique login ID and password for each service is much more secure.
