You can hack FaceBook, Twitter, Youtube and Amazon accounts of users connected to wifi network. FaceNiff is an Android app that allows you to sniff and intercept web session profiles over the WiFi that your mobile is connected to. It is possible to hijack sessions only when WiFi is not using EAP, but it should work over any private networks (Open/WEP/WPA-PSK/WPA2-PSK). It also works on WPA2. FaceNiff works by capturing all the packets that are sent back and forth inside the network. It will wait for a user to login to FaceBook or other services, and will intercept the data and display the user’s login ID. By clicking on it, hacker would be able to log in and take over the account. Beware.