If you didn't download it intentionally, avoid opening it.

The Mystery of the String: Identifying "8604013-dcb211ce34448acc6017969e709b650a.mov"

Allows browsers to store the file locally; if the name changes, the browser knows there is a new version.

Use a tool like VirusTotal to upload the file (or its hash) to see if it’s been flagged by security vendors.