The Swine flu viruses are trying to take control. You have to kill the virus with the antivirus. First protect your antivirus from the virus. Click on the virus and hold to make the antivirus grow and release to kill the enemies.
Use the mouse to guide the antivirus. Left click and hold to make the antivirus grow and release on the virus to killl them.
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.