It's definitely possible, and you don't need to be a genius to do something like that either. Now, someone could break into your house and bug your phone while you're out ...but is that very likely? ...prooooobably not. We don't worry about that, because it's unlikely that anyone is sufficiently motivated, or has the means to do something like that without getting caught. Was the USB infected? I'd guess probably not. And, I'd hope OP would know if the guy was that kind of person... BUT, what if it was? And yes, I'm being more paranoid than the typical person, but that's only because this is my field so I know what's possible.