Virus clouds resemble asteroids. They have a dark white/grey inside with many visible black splotches. On it are some smaller rock like objects. The edge of the cloud's is white. More than three variations of virus clouds exist.
Virus clouds are spawned into levels, like Items. They are only spawned when random matter is spawned. Two virus clouds are spawned per level, spawned at the corners or the levels. Since random matter is placed randomly around the level, the player cannot be sure where it will be. Virus clouds are present so that the player can head to these and reside in them to be safe, as random matter is never found in virus clouds.
Random matter acts only like scenery, only marking out the area a player can head to be safe. All enemies can go into virus clouds and drop/shoot their weapons through it. It disappears once random matter disappears. Although random matter of different sizes is seen on the menu, all virus clouds are close to the same size.