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