In most circumstances, a full video downloader is not illegal to use in and of itself. However, the downloading of videos from popular video-streaming websites may breach the terms of service and, in certain cases, infringe copyright laws. The situations in which copyright may be infringed are summarised on iSkysoft.com.
An article on PC Advisor draws attention to the fact that many of the largest sites that provide video content are owned and operated as commercial ventures, and as a result rely on the revenue generated by advertisement set alongside or within video content. By downloading videos, users can drastically limit their potential value. To protect against this, websites like YouTube.com present terms of service in which users accept that videos be viewed solely by means of streaming.