: Use VLC Media Player or MPC-HC. These players handle almost any codec found inside an MKV container.

: MKV files themselves are rarely malicious, but "double extensions" (e.g., AgADvQADvXFxVw.mkv.exe ) are common ways to hide malware. Ensure your file explorer is set to "Show file extensions" to verify it is truly just an MKV.

: Avoid MKV files that immediately trigger a popup asking you to download a specific "codec" or "player" from a random website; these are almost always phishing attempts.