You are the firewall and have to save your computer against the viruses. Try to catch as much as you can. But be careful: Let pass the security updates to save your computer. Otherwise you will be incapacitate and can do nothing for few seconds
Right / Left -> Control the firewall
A context menu should be shown when right-clicking or, on touch devices, long-pressing in the game. This menu especially allows to play in full screen and control the volume.