Beware of "Who Viewed My Profile" Apps on Facebook

Facebook does NOT track who views whom.
Check it : http://www.facebook.com/help/?faq=12903

But some third-party applications offer this feature (Try at your own risk).
There are applications you can install on Facebook that claim to provide this option, i.e. that you can see who has been looking at your profile. Some of them publicize themselves to make it sound like they're helping you identify if you're being stalked by someone. Others are probably just appealing to a natural curiosity that people have about who might be checking them out.

You can only get this information if you actually add the application to your account and explicitly give permission for it to do so. So, on the face of it, it sounds harmless. But there are three serious issues related to what seems to actually be happening:

They're publishing the information to other people. Unlike with LinkedIn, where only you can see who has been viewing your profile, these FB apps are sharing that information with your friends, which you may not have expected when you gave them permission to access your account.

In some cases, they're publishing images to your Photos page that shows the profile pics of several of your friends and a comment—supposedly from you—that says, ""Try it, really works!!". It also includes a link to a page that I'm assuming either tries to get you to add the app yourself, or worse. (I won't click on it myself to see what actually happens...) Then, if one of your friends has his/her notifications set up to get an email whenever they're tagged in a photo, they get alerted to this image.

• In another case I'm aware of, the person's friends received a posting on their Walls saying, "X has checked your profile", which is not only the opposite of why you would add the application (you want to know who's looking at you, not tell people you're looking at them), but also...

• The information isn't true. In the first case, above, a friend of mine was tagged as being one of the top viewers of another person's profile even though s/he hasn't done so in months and certainly never did it frequently. In the second case, the person hadn't recently looked at any of the profile pages of the people who suddenly got notices that s/he'd looked at them.

  I don't know how these apps determine who they claim was doing the viewing, but it's quite possible they're just randomly picking people from your list of friends (which all third-party apps have access to because Facebook unilaterally decided this is "public information.")

• Your friends have no way of opting out of this. As mentioned above, when you add an application, you're not just giving them permission to access your information, you're giving them permission to access a certain amount of your friends' information as well. While people can set some restrictions on what information their friends can share about them^*, they can't prevent you from sharing at least their name and profile picture. The only way to prevent seeing their names show up in these locations would be to unfriend you altogether—which is probably not something you were intending when adding the app in the first place.

• So all that to say that these applications are not providing some wonderfully helpful service to you. They're scamming you by mining data that they could use to sell to marketing organizations—legitimate or otherwise—or for even more malicious purposes, such as spreading viruses and other malware.

  Facebook has been removing some of these applications as they find them but your best bet is simply to avoid them in the first place. Don't click on links to pages that you don't know where they're taking you and don't add applications that you haven't checked out first (e.g. legitimate references from friends).