How Crackers Are Caught?

Hi,

let's talk about facts, I know there are tons of ways to catch a hacker but what about a virus 'creator' / 'author', is it possible for them to get caught?

and I wanna clarify if it is really possible that you can upload a virus if anyone just simply visits your site, well how is it possible?, can you use php and say that " if someone visits this site upload this file to the victim's PC without him/her knowing " ?

thanks