source: http://www.securityfocus.com/bid/1219/info

Large usernames or passwords sent to the router's HTTP interface restart the router. Router log will show "restart not in response to admin command"

Open the router interface with your browser.
Username: ......................... (x79 +)
After the router restarts, you can hit refresh on your browser to take it down again. 

A simple script or program could be written to keep the router down indefinately.