Wifi password randomly changed - Discovered a DoS Attak: Ping of Death at the same time

Hello,

I was working recently and noticed I was randomly kicked off my wifi. I hard-wired into the router and saw that the password had been chagned! I looked at the activity logs and saw a Dos Attack Ping of Death at basically the same time I was forced off the wifi.

Obviously now I have changed my SSID password. What else can I do to prevent this? My firmware is up to date (V1.02.02).

How come the router was able to detect and recognize this old style of attack but couldn't do anything to stop it? 

Thanks!