Hi. I just stumbled across this forum while searching for the same IP address. I have the DIR-655 w/ 1.33NA FW with SecureSpot disabled, and the log is still showing that IP several times per day. I've also had several router timeouts, requiring a manual reboot (power cycle) to get it working again. It belongs to Charter Comm and is the router I've been using for 2.5 years. The problem really started getting bad when I upgraded to their 50 Mbps service. Not sure if the two problems are related...
It looks like there's some useful information here that I can try. I'll post my results when I have them.