In yet another shoot-first-ask-questions-later move, the site has implemented the change it first announced - very quietly - in April, when the company said it was synching users' names with their automatically assigned Facebook e-mail addresses.

But what's got the Internet a-twitter is that Facebook never said it would automatically replace the contact e-mail you had already posted.

Facebook's only comment about the change, as told to the tech blog Mashable.com, was, "We've been updating addresses...to make them consistent across our site."

To see the change, visit your profile page and click on "About," then check your Contact Info section.

Your Facebook e-mail address shows up there and on your Timeline even if you've previously hidden any e-mail addresses you've provided. (For users who never chose a vanity URL - such as facebook.com/[yourname] - the site has assigned a numeric e-mail address.) E-mails sent to the address show up in the message inbox on the site.

Users can easily change their e-mail back by clicking "Edit" in the Contact Info box, then hiding the new address.

This isn't the first time Facebook has opted users in to a new feature they didn't necessarily want. Timeline, social ads (also called "sponsored stories") and automatic notifications from "liked" pages are just a few the changes that have irked the site's nearly 1 billion users.