With all due respect Emma, you really are going to have to resolve this 'brother' situation, otherwise, all hell is going to break loose eventually.
What I suggest you do, is to cut his bloody hands off!! That will cure it!
Seriously though, ensure that the puter is housed in your bedroom, for example, and then put a secure lock on the door....He can always cut the cabling to the rear of the box, if he is that vile....