The app requires root access on the user's Android smartphone, but other than that it's fairly simple to use, which makes it perhaps even more dangerous than Firesheep, a Firefox extension that lets users hijack Facebook and Twitter sessions over Wi-Fi networks. FaceNiff also works on WPA-encrypted Wi-Fi networks, which Firesheep doesn't support.
While we're not suggesting that any of our readers should use the app to hack someone's account (it might even be illegal depending on where you live), the sheer fact that such an app exists and is very easy to use means you should be extra cautious when connecting to public Wi-Fi networks.
Recently, we wrote about the necessity of using HTTPS, which offers a fair degree of protection against attacks such as those from FaceNiff and FireSheep. If you still haven't switched to HTTPS connection on all your favorite web services that support it (both Facebook and Twitter have the option), we recommend you change your settings right now.
Besides Facebook and Twitter, the latest version of FaceNiff also works with YouTube, Amazon and Polish social network Nasza-Klasa.