Did you find it or did you buy it? If you found it, as you said first, you should try to return it to the rightful owner. If you bought it, as you said second, you should contact the seller and ask where they got it...because there is a good chance it is stolen. Fortunately, Apple has implemented this measure to prevent thieves from using stolen iPhones, and more and more people are aware of this and are not buying stolen iPhones. As a result, iPhone theft has dropped dramatically.