Gatekeeper warning when trying to open video files

Matt T

macrumors regular
Original poster
Dec 1, 2005
171
9
Australia
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.
 

MC6800

macrumors 6502
Jun 29, 2016
368
126
The "unidentified developer" warning is actually referring to the app it has chosen to open those video files with (based on their extension), not the files themselves. Do a Get Info on one of those and see what app "Open with" says. Most likely they're pointing to one of your apps that you haven't run since last updating the OS. You can change them all to open with your favorite viewer app there in the Get Info.
 

Matt T

macrumors regular
Original poster
Dec 1, 2005
171
9
Australia
The app I use is VLC, which is what is listed under the Get Info window. I get a similar warning when I try to open the same videos in QuickTime player (the QuickTime warning gives me the option to open the file anyway, while the VLC warning doesn't). I don't remember installing any updates for VLC recently.

Edit: plus I'm not sure why, if the warning was related to the app, why it would only appear when opening certain files. Shouldn't it appear for all files if that were the case?
 

Matt T

macrumors regular
Original poster
Dec 1, 2005
171
9
Australia
Thank you but I understand what the warnings are for, it just seems strange they would randomly begin appearing for video files.
 

Matt T

macrumors regular
Original poster
Dec 1, 2005
171
9
Australia
Just to close the loop here - I ended up reformatting my Mac and restoring copies of these videos. The warning no longer appears.

Very strange but it seems like it may have been some kind of bug or corrupt file somewhere?
 

thomasareed

macrumors member
Aug 24, 2015
88
89
Well, it's impossible to know what may have been going on at this point. Malware sometimes masquerades as video files, so this could have been malicious... but we'll never know at this point.
 
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