A virus is the human race. The human race is cutting down forests, melting polar ice caps, and destroying the world.
And that's why the hippies and tree huggers basically died out in the 70's because, once again, the human race is a virus and is destroying everything in it's path.
Either
1.A common disease plague that harms human health resulting in multiple symptoms that makes us sick.
Examples are:
-Common cold
-Measles
-Chicken Pox
2.A random code that harms computer system and data by means of copying it self and duplicating it until your computer can no longer run properly.
An organism that moves around until it has found a single, empty spot and stays there and mutliplies until every natural resourcein the area is consumed, and then moves on to consume another area.
See human.