O.O they can see my last name?
Kidding, but um can't they just put a fake last name?
and what about account verification?
Since only the user can see the name put in the box, we can easily ask someone trying to claim the account as theirs what they put as the last name.
Alternatively, if they put their actually last name, our billing team can cross-reference it with any purchases they may have made with credit cards/debit cards/paypal/etc.
But mostly its just a nice text box for people who want to put their name somewhere.
Can you enter a fake name? Yes, but it isn't going to help you out much.