Files with the “.mov” or “.qt” extension are movies in Apple’s QuickTime video format. To play these files on Windows, you must have the free QuickTime Player installed. On a Macintosh, you can usually just double-click the files to play them since most Macs come with QuickTime installed.
Windows users may be interested in QuickTime because QuickTime Pro allows you to very easily cut-and-paste video, so you can edit video files just as easily as you can text.
QuickTime files cannot contain viruses, so there is no harm in downloading them, or opening them if somebody emails you one.