- "Every mammal on this planet instinctively develops a natural equilibrium to the surrounding environment, but you humans do not. You move to an area and you multiply. And you multiply until every natural resource is consumed. The only way you can survive is to spread to another area. There is another organism on this planet that follows the same pattern. Do you know what it is?...a virus."
- ―Agent Smith compares humans to a virus [src]
A notable virus was Smith, a former Agent gone rogue, who had the capability to copy himself onto redpills, bluepills, agents and other programs alike. Smith, ironically, despised viruses during his time as an Agent.