i have absolutely no idea what a pokevirus is so could someone tell me
Unlike other status ailments, Pokérus cannot be healed at a Pokémon Center or with any status ailment healing item, and can only be obtained by the Pokémon in question once. When a Pokémon has the Pokérus, it gains double the effort values from battling (i.e., fighting a Magikarp will give two Speed EVs, rather than one). Effort points gained from vitamins are not doubled. The infected Pokémon can infect other Pokémon with the virus for a period of about two days. However, the Pokérus timer can be delayed by several methods including placing the infected Pokémon in a PC box.
-Bulbapedia
There is a 3 in 65,536 (about 1/3 of the chance to encounter a Shiny Pokémon) of enountering it on a wild or newly hatched pokemon.
Pokerus doubles your ev's
For example normally if you beat a Lilipup you would get 1 attack ev but with pokerus you will get 2 attack ev's