What Caused the Glitch?
When someone uploads his/her contact list or address book to Facebook, Facebook tries to match the information in the contact list or address book to other people on Facebook in order to generate “friend recommendations”.
The “friend recommendations” is a list of users that you see on the right side of your Facebook account that Facebook asks if you want to add as friends.
It is this "friend recommendations" that inadvertently stored the contact list or address book information for other Facebook users that the owner of the contact list or address book has some form of connection or relationship with.
If the persons who this information were inadvertently stored to their accounts, use the Facebook Download Your Information (DYI) tool to download an archive of their Facebook accounts, they may end up with additional email addresses or telephone numbers of other Facebook users who they have some form of connection or relationship with.
Facebook have since fixed the glitch and enabled the Download Your Information (DYI) tool that was disabled because of the glitch.
Facebook claims that they have no evidence that this glitch has been exploited maliciously and have not received any complaints from users.
For more information about this glitch, click here.