It comes with OpenCandy - an installer which bundles legitimate applications with offers for additional third party applications that may be unwanted by the user.
I use 4kdownloader. I have tried some but find 4kdownloader the best. 4kdownloader gives mp4/mkv/flv/3gp videos & mp3. Its just that I found Ummy & dont know its safe or not, so asked here.
Most of these YouTube downloaders are fishy to begin with. =V A little recommendation, check the software whether or not they are listed on popular download hosting websites (Softpedia, MajorGeeks, SnapFiles, DownloadCrew, etc) and if they are, see if there is a warning mentioning if the software contains bundles in the installer package. They usually give such (very helpful) notifications.
I guess this is one popular online site to download Youtube videos. http://en.savefrom.net/1-how-to-download-youtube-video/ On this site Ummy Downloader is mentioned. I couldn't find it on popular download site.