Android: We heard about WiFiKill a while ago, but it just seemed too, well, evil to write about until now. The app disables the connection of other devices on the same Wi-Fi network; essentially you can bump people off without them knowing.
WiFiKill is designed to take revenge on bandwidth hogs who are slowing down your network. As developer bponury describes it on the XDA Developers forum:
So if someone (anyone) is abusing the internet wasting precious bandwidth for a Justin Bieber videoclips you could just kill their connection and stay happy with a full bandwidth just for yourself.
The app works only with rooted phones and works, similarly to FaceNiff, by spoofing ARP replies to trick other devices on the network into thinking your Android phone is the router. WiFiKill then drops all their network packets. To the victims, it still appears as if they are connected to the network, but the Internet just appears to have stalled.
Besides pranking people, pure selfishness and meanness, WiFiKill might have some use for controlling devices on your own network. For example, if you're a small business owner and you don't want to allow your staff to use the Wi-Fi network during certain hours, you or your IT admin could kill their connection (of course, you could do this from the router too, but perhaps you want to do it from your phone). Perhaps you're a parent and want to cut off an errant teenager's Internet access.
Just as we've seen with network sniffing tools, WiFiKill also demonstrates weaknesses in Wi-Fi security, so I guess the app could also be considered educational.
The app, however, was considered too evil for Android Market and Google pulled it, so you'll have to get it from the XDA Developers forum. (Try not to be too evil with your power!)
Lifehacker's Evil Week is all about topics such as password cracking, social hacking and other questionable tricks to make sure you're in the know. Knowledge is power, and whether you use that power for good or evil is in your hands.
WiFiKill [XDA Developers]