I have lent my old Macbook Air to my friend who will be giving it back to me shortly. He was desperate for a computer and I had just bought a new Macbook Air (the old one had a few issues with it but he seemed perfectly happy with it). However I don't want to have his old data on the computer as I have no interest in his personal details. So is it either a) possible to go to a 'return to factory settings' option or b) can I use the Time Machine to just return the contents of the MacBook Air to what it originally was; when I got my new one this is what I did - simply copied the old MacBook Air to the new one, but will this mean I won't be able to see anything he's downloaded onto his machine? I'm not expecting there to be anything dodgy on there but I would rather respect his privacy!