Codemasters have now closed GRID online servers... but all is not lost, you can still play multiplayer via LAN, but also you can use the LAN mode to play over the internet with friends using a free VPN style app called Tunngle. Works for most LAN capable games too :p
Link Removed due to 404 Error
Tunngle for LAN over web tunnel...
Just come across this app Link Removed due to 404 Error
Basically does much the same thing as Hamachi however...seems to work better for a few titles that wouldnt work at all over hamachi/LAN modes...
At the minute its German as its still in beta, but seems...
beta
direct chat
discretion
encryption
file sharing
friends
game lobby
lan
local network
networking
online gaming
pc games
performance
privacy
secure connections
tunngle
user control
virtual network
vpn
web tunnel