[MovedGoalPosts]

If he is a serious geek and doesn't play nice then eventually any networked computer can probably be hacked.

However, if you have a software based firewall on your computer, you have your computer set with a reasonably strong password for all the accounts used on it, requiring those accounts for log in,, you don't have file sharing enabled, you will be reasonably secure. After all if you trust this person enough to rent a room in your house, he is reasonable isn't he?