This is part of an email from facebook about the bug:
we recently fell short of our goal and a technical bug caused your telephone number or email address to be accessible by another person.<p>The bug was limited in scope and likely only allowed someone you already know outside of Facebook to see your email address or telephone number. That said, we let you down and we are taking this error very seriously.
Describing what caused the bug can get pretty technical, but we want to explain how it happened. When people upload their contact lists or address books to Facebook, we try to match that data with the contact information of other people on Facebook in order to generate friend recommendations. Because of the bug, the email addresses and phone numbers used to make friend recommendations and reduce the number of invitations we send were inadvertently stored in their account on Facebook, along with their uploaded contacts. As a result, if a person went to download an archive of their Facebook account through our Download Your Information (DYI) tool, which included their uploaded contacts, they may have been provided with additional email addresses or telephone numbers.<p>Here is your contact Information (inadvertently accessible by at most 1 Facebook user):
<i></i><i></i>@<i></i><i></i><i></i>.com<p>We estimate that 1 Facebook user saw this additional contact info displayed next to your name in their downloaded copy of their account information. No other info about you was shown and it's likely that anyone who saw this is not a stranger to you, even if you're not friends on Facebook.