1. A method for authenticating download of a digital content file ordered from a web site, the method comprising: receiving a selection of the digital content file with the web site; calculating a first code indicative of the digital content file, wherein if the digital content file is changed, the first code is likely to also change; sending the digital content file to a client computer; sending the first code to the client computer; and re-sending the digital content file if the client computer determines the first code doesn't match a second code calculated by the client computer after the client computer received the digital content file.