It will be your router that is responding to the ping unless you have it forwarded to a specific internal PC.
To be honest, I would not worry over your machine responding to ping. All it is saying is that the IP address you are using is valid. What happens is a hacker would then run a port sweep to see if you have any specific ports/applications running on the standard ports. If you are locked down then they will move onto somebody else.
But how many people are still paying for a software firewall when they have a perfectly good router that can flter out the garbage. I think most people with routers setup their wireless, setup their wireless encryption then forget about everything else, shame really.
Why is your REP black mate??