Is it possible that some hacker is logged in to my computer?
Nope. Both of those are you.

console is where you've logged in (likely on startup), and the GUI started up.

s000 is the first shell you opened, the Terminal window itself. If you look at the WHAT column, it shows the last command run in that shell (w), which you just did.

So it's the same user (you), logged into two sessions, one for the OS X GUI, and once in that shell in the Terminal window.