If a person did such a thing, how would you as the owner of the computer be alerted to such, including finding out said username?
If such a thing happened, what sort of recourse would you have (ie discovering the identity of the person and nailing their ass to the wall)?
Yes, I know I'm waving my ignorance around for the whole world to see, but my usual sources of such information have let me down. And I'm not so proud that I feel I have to hide how much I don't know. Links to things I can study myself are fine.