Defend your server's firewall using virtual arsenal to prevent the waves of virus from destroying the server's firewall. Your defense consisted of a variety of stationary emplacements along the network path, By strategically choosing, placing, and upgrading towers you just might be able to destroy the viruses before they reach the firewall. You can hold down the shift key to build multiple towers of the same type. Hold down spacebar to see the life meters of all the viruses.