1. MAC: install HoRNDIS (http://joshuawise.com/horndis) (only once)
2. MAC: make sure that wifi is enabled but not connected to any network (might not be necessary, not sure)
3. Connect Android<-usb->MAC
4. Android: enable USB tethering
5. MAC: .enable internet sharing (sys pref->sharing)
share from "your android device" to computers using Wi-Fi (or/and Bluetooth PAN)
.set Wi-Fi options: security
