The app is free and notifies you whenever someone removes you from the Facebook friend list. But it asks for your sign in and password.

"Looking at a Wireshark log for this check however shows that the login credentials are not sent directly to Facebook but to yougotunfriended.com," security firm MalwareBytes said.

The app also displays ads and can install malicious software on the user's computer. What's more worrisome is that it doesn't show up in the apps list on Facebook. So you can easily forget that it is there and monitoring your activities.

Expert recommend removing the app and changing your password. There have been other apps in the market that alert the users when a Facebook friend ditches them, but this new app seems to be designed to steal passwords.