The stupidest thing you can possibly do on the Internet is to use the same user names and passwords for the different online platforms and services. Then how come we keep repeating it all over again, with the self-destructive stubbornness? We are either too lazy or unforgivingly ignorant about the cyber security.
Finally, someone has decided to do something about it. What exactly and how efficiently? Well, the Facebook has decided to turn the first page. If it turns out that you are using your Facebook account user name and password for some other web service, you will get a fair warning to change them accordingly.
How the Facebook knows all of that? You should relax. If Facebook knows it, then you can rest assured more than one hacker knows it, as well. It is always better to change them all before any real damage is being done. On the other side, do not worry about your privacy. Facebook works for you, in this case.
Do we have to repeat it all? User name and password twins on the Internet are not a smart choice. Do not be lazy and at least create different passwords, if you do not have enough patience to play with the different user name combinations. Our hats off to the Facebook for this thoughtful move.