Facebook users are freaking out over the fact that the numbers of all their cellphone contacts are showing up on Facebook. What's going on? Is Mark Zuckerberg planning the world's largest phon-a-thon?

A scary message is being passed around Facebook, warning that you and all your buddies' cell phone numbers are visible to the world. It goes something like this:

"OMG this is for real everyone!!!! Warning to ALL …ALL THE PHONE NUMBERS IN YOUR PHONE are now on Facebook! No joke – go to the top right of the screen, click on Account, then click on Edit Friends, go left on the screen and click Contacts. All phone numbers are published!! Please re-post this on your Status, so you r friends can remove their numbers and thus prevent abuse if they do not want them published."

Unlike most wackjob viral Facebook status updates, this is partially true. If you've downloaded one of Facebook's smartphone apps and let it sync your phone contacts with Facebook, the app automatically sucks up all the contacts in your phone and puts them in your Contacts list. If you're logged into Facebook your Contacts list is here.

So, all the phone numbers in your cell phone are technically "on Facebook." However, the numbers aren't visible to the world and/or stalkers—they're only visible to you, when you click on the Contacts page. "The phone numbers listed there were either added by your friends themselves and made visible to you, or you have previously synced your phone contacts with Facebook," Facebook explains in a rumor-debunking post. "Just like on your phone, only you can see these numbers." It's a bit jarring to see this big list of phone numbers of people you barely know, but this isn't an ALL CAPS-WORTHY SITUATION.

Facebook points out that the feature is not new, as if the fact that it's been around for a while means it has to be benevolent. In fact, when the feature was first rolled out in January of 2010, critics pointed out that Facebook is essentially jacking your friends' phone numbers and uploading them to their servers without their consent. Even if they don't display them to anyone but you, they've still got these peoples' names and numbers, as well as their connection to you. All valuable data going forward—and chances are you did not read the mind-numbing message that informed you this was going to happen when you installed the app in the first place.

So, there goes another data pile, up into the Facebook machine. The fact that Facebook has been pushing to make user phone numbers available to third-party app developers should also concern you if don't want that person you made out with once at the bar whose number is still in your phone, for some reason, to start getting texts about your withering FarmVille crops.

Every privacy outrage, legitimate or otherwise, is a reminder of just how much information we're giving to Facebook. If this latest one makes you want to share a little less, you can deactivate the Contacts feature here.

[Image, top, via Shutterstock.com. Screenshot via ITworld]