Facebook users eager to install a "Dislike" button on the social networking site have fallen victim to a so-called "rogue application" that hands scammers access to personal information, and signs up unsuspecting users for monthly cell phone charges. (See the "Dislike" button at work.) How did this happen? 

What's a "Dislike" button?
Facebook has a button that allows users to "like" their friends' posts, photos, and updates, but no button to register disapproval. The scam claims to offer a way to "dislike" annoying content. 

How did people get scammed? 
A link pops up in a friends' Facebook feed saying something like, "Get the official DISLIKE button NOW!" Those who clicked on the link are asked to download an application which in turn directed them to a series of online surveys. Installing the app gives the scammers gullible users' personal details, while filling out the survey automatically signs people up for a $5-a-month cell phone charge.

And do you get a "Dislike" button at the end of all that?
Yes, you do — but one that is freely available online without filling out surveys. FaceMod, which designed the Firefox add-on, says it has nothing to do with the scam. About 600,000 people have safely downloaded its "Dislike" add-on to date. 

Did many people fall for this?
"Tens of thousands" of Facebook users have clicked on the application, according to online security firm Sophos, in the hopes of getting a "Dislike" button. Once people click on the link, it is automatically re-posted on their Facebook pages with a personal endorsement. The idea is to make their friends think it's legitimate, so they'll click, too. The scam capitalizes on the very real demand for a "Dislike" button — over 500,000 people have joined a Facebook group requesting the site to add an official one

Why doesn't Facebook just create its own "Dislike" button?
Mark Zuckerberg, the 26-year-old founder and CEO of Facebook, said in July that the company would "definitely think about" adding one. But social media experts say it would be inconsistent with Facebook's ethos. It creates the potential for "somewhat negative experiences," says Justin Smith, editor of Inside Facebook, quoted by ABC News. "If content is posted by a user and it ends up being disliked, that might be an experience Facebook might not want to officially support."

This isn't the only Facebook scam, is it?
No. There's even a term for the practice: "clickjacking." Many rogue applications try to suck you in with "shocking" videos of celebrities like Justin Bieber, or offers of free iPads. And the problem appears to be growing, as there has been an "upswing" in the number of scams lately, warns Riva Richmond at The New York Times.

How can I avoid these Facebook scams?
Use a "pinch of skepticism" when clicking on your friends' links, says Jared Newman at PC World. Check the bottom of the posting, and you'll see if it came from a third party application. Or just look out for the "other trademarks of scams," says Rob Pegoraro at The Washington Post. That is, "EXCESSIVE capitalization and too many exclamation points!!!"

Sources: New York Times, ABC News, PC World, Washington Post, Sophos