Why are you afraid of malware? You can’t get any malware by downloading a mkv file (or an ISO file if you’re trying to get the AVCHD or the DVD version). If you’re afraid of some harmful ads on the torrent tracker site you want to use, just don’t click on them 😃 Or even better use a browser which has an ad blocker, e.g. Firefox with the AdBlock addon.
There are 2 alternatives how to get it