For those of you who are worried about certain tools that sniff your data and prevent you from accessing a wifi network, you can defend yourself with this simple app from XDA forum member gurkedev.
Wifi Protector is an Android security app especially designed to detect and prevent ARP poisoning attacks against your phone in Wifi networks.
The app runs a service on your Android device that continuously monitors network-related parameters. When abnormal behaviour is detected, an alarm is triggered. The type of alarm can be configured and detection and alarms work on non-rooted phones. On rooted phones, it is also possible to reconfigure the phone to make it immune against the attack.
XDA members can download the app for free in the application thread, or feel free to donate by downloading the version in the Android Market._________