6010.mkv.mp4 -

A common tactic for malware is to use a double extension like .mkv.mp4 or .mp4.exe .

Some software, when converting an MKV to MP4, might append the new extension to the original filename without removing the old one, resulting in filename.mkv.mp4 . 6010.mkv.mp4

If the file won't play, you can use the VLC Media Player, which is known for handling almost any video format regardless of extension errors. A common tactic for malware is to use

If you are looking into this because you need to play or edit the file: when converting an MKV to MP4

A more universally compatible format supported by almost all devices and platforms.