Sneaky Facebook apps
If you give a website or Facebook app access to your Facebook account, the site or app may start posting updates to your feed automatically for you. For example, Pinterest.com will post the images you’ve pinned and the Washington Post Social Reader will share what articles you have read.
When you grant Facebook access to a website or app, make sure to read what the site/app will be able to access and what they will share before you give your permission.
To change your app settings or remove access for an app: login to Facebook, click on the arrow in the top right corner (next to Home) and choose Account Settings. Then click on the Apps link in the left column. Click Edit next to the app if you want to change it’s access settings, or click the X if you want to remove access entirely.
More info about how Facebook Apps work