The ASUS RT-N13U home router comes configured with an unsecured telnet for user "admin".
Telnetting in with this user will result in a root shell. The telnet is not configurable from the web interface, nor does changing the password on the web interface's admin user make any difference. I have alerted ASUS to the problem on 10/25/13. I have been able to verify that this telnet interface is visible from both the LAN and WAN.
Sincerely,
Shellster