Good answers here are anything that shows you he’s a computer/technology/security enthusiast and not just someone looking for a paycheck. So if he’s got multiple systems running multiple operating systems you’re probably in good shape. What you don’t want to hear is, “I get enough computers when I’m at work…” I’ve yet to meet a serious security guy who doesn’t have a considerable home network–or at least access to one, even if it’s not at home.