This can be a tricky question. The interviewer is basically asking why you are leaving your current company while also probing to see what benefit you might be to their employer, as well as how much you already know about the company itself. Be careful in offering up too little information about how you would benefit the company. Be specific about how you can fill a need within their company based on your experience or expertise. If you do not know much about the company, try to be as thorough as possible and remember to research in more detail for future interviews.