A denial-of-service attack (also, DoS attack) is an attack on a computer system or network that causes a loss of service to users, typically the loss of network connectivity and services by consuming the bandwidth of the victim network or overloading the computational resources of the victim system.

For online games the threat is enormous : if someone manage to attack the game servers succesfully, then no player can enter the game, or all players that were playing are kicked out of the game because the game server has crashed, anyway the Online Game Industry is in great danger with Denial of Service attacks.