Alternatively, they might be looking for free MKV files, like public domain content or creative commons videos. In that case, there are legitimate sources where you can download such content. I should mention those options to guide them towards safe and legal alternatives. For example, sites like Archive.org or Internet Archive have a lot of public domain movies and videos available in MKV format. YouTube to MP4 converters could be another alternative if they want to convert videos they have the right to download.