: If the file is already on your system, run a scan using Windows Defender or Malwarebytes before attempting to play it.
Where did you encounter this file name, and are you trying to or identify its source ? video-18mp4
: In many cases, files named with unusual extensions or suffixes like "video-18.mp4" or "video-18mp4" are found on unreliable streaming sites or in spam messages [1, 2]. These are often used to trick users into downloading malware masked as a video file [2]. : If the file is already on your