Recently when trying to open some video files on my Mac I'm getting a Gatekeeper warning that the file cannot be opened because it is from an unidentified developer. It only seems to be affecting video files saved in a particular folder and only files with an .mpg extension (other video files with avi/mp4 extensions in the same folder open fine). I'm concerned that if I bypass these warnings I might be executing some kind of malicious code. I've downloaded Avast and MalwareBytes but neither of them detected any threats. What can I do to ensure my files are safe? Silly me I haven't kept a backup of this folder.