Many of us might have authorized permissions for various free apps to access our private information in our online accounts, such as in Facebook, Twitter, Google+, Yahoo, LinkedIn, DropBox, Instagram, Flickr, etc. As matter as fact, it has become common that not all those apps were useful. However, we just left them there, keep being authorized to get our private data as much as they want 😀
Wanna recheck and clean those permission? Try visiting mypermissions.org. They have provided useful links for you.