I think I've found a bug. When You use john to decrypt WPA cap (I used it with both letters and numbers, but I doesn't think it matter), then You manually close xterm window, where decryption is going, aircrack-ng is *still* running - without any window You can open/close/whatever. It's also consuming 80-90% of Your CPU time, on 900 mhz Have to kill it via xterm using PID.