How can someone prejudge someone with background information on that person?

Doesnt prejudging mean to judge someone beofre you know them, so how does basing it off of someone's background prejudice. Background is information, so how can thinking about it beprejudging?How can someone prejudge someone with background information on that person?looking up info from their pastHow can someone prejudge someone with background information on that person?I think it means judging them from information you have heard about them, but before you have gotten to know them personally. For example, if you hear that a girl you work with has slept with several guys recently, but you haven't talked to her much and still judge her as promiscuous, that would be prejudging based on background info.