This is common in hand-reared kittens, as they don't get the feedback from their littermates that they are being too rough. Try to recognize the situations when he attacks (such as when you walk past), and keep a toy in your pocket to divert his attention. When he attacks, squeal and pretend to cry (so he knows it hurts), but try to avoid moving or pulling away, as this arouses his hunting instincts and will make him attack more.