After updating to Sequoia 15.3, all MP4s on my system give malware warning

"So I can open VLC and open an mp4 file from VLC, but if I try to open it in VLC using the mp4 file drop down menu the very same mp4 file suddenly becomes a threat that might (it just might) install malware on my Mac!?"

Select one of the offending mp4 files, and press Command-I to open the Info window.

Under Open With, select VLC (or other video playing application of your choice), the click "Change All".

Then try again. Does the problem remain?

There has been a change in macOS Sequoia that affects these files.

In order to open a file directly with a double-click, you need to have installed an app that has already advertised support for opening that file. Most importantly, you must then use that app to open those files.

Other people reported this problem with SRT files. I couldn't reproduce the problem because I had VLC installed, which properly advertised support for SRT files. But then if I manually changed the Get Info > Change All setting in order to open the files with BBEdit, I would get the malware error message.

What this means:

1) Any file is now treated as potentially an executable document. Double-clicking a file opens that file and potentially executes it. macOS will only allow double-clicks on files that it knows how to handle, either the file is a properly signed executable, or you have already installed an executable that properly handles the file.

2) You cannot change the "Open with" setting anymore, at least not like you could before. If you have two or more apps that properly advertise support for a given type of file, then you can choose between them. But you can't manually chose other apps. There is no guarantee that those other apps will support the file unless they have already declared that they can handle the file.

3) You can always open these files from other apps via File > Open or (sometimes) drag-n-drop.

ManHasAspirit wrote:

This appears to be the answer. Can anyone advise a simple app I can use that has "advertised support for" .srt files as @etresoft mentions so that I can just double click .srt files again?

VLC supports them, but only as subtitles, not for editing.

It's an interesting problem. Building a simple text editor that opens SRT files would be trivially easy. But it's so easy that anyone could do it, and release a free version. It's a race to the top. The only way to complete would be to add features and more functionality. But it's an SRT file. How many users would such a tool have? And of those, how many would be willing to pay money? So before a developer writes the first line of code, the race turns around and goes to the bottom. In the end, you get nothing. The beauty of open source software.

Clyde Graham wrote:

I updated my 2024 Mac Mini to Sequoia 15.3 last night, and now every single MP4 I have gives a "Apple could not verify...mp4” is free of malware that may harm your Mac or compromise your privacy." and my only options are Done or Move to Trash.

They will play (in icon) if I click the play control, but will not open in VLC or QuickTime Player.

These are files that in some cases I have had for years. Nothing has changed other than updating to 15.3. Do I have any options other than waiting for Apple to address this? Is there a way to rebuild the desktop database or whatever they're looking at here. This is crucial for me professionally.

There maybe a correlation with VLC(?) If those files are set to open by default to VLC try changing that

mp4 "can’t be opened because it is from a… - Apple Community

ref: Apple can’t check app for malicious software - Apple Support

Command i opens the information pane.

ManHasAspirit wrote:

I'm trying to support the original post, and it seems to me that the likely explanation is that recent updates of Mac OS are disassociating extensions from applications

Sounds like the OP issue was resolved above...

you can file a bug report / submit your Apple Feedback here:  Product Feedback - Apple

The current stable release of Sequoia  including bug fixes,  security updates  is macOS 15.4

Keep your Mac up to date - Apple Support

Keep your Mac up to date - Apple Support

Update: I have found that using Get Info to assign a.SRT file to TextEdit does not solve the problem for Files downloaded from the Internet. Yes it does solve the problem for that individual file but any future files downloaded from the Internet will still give this error shown in my screenshot:

i'm also showing here the website that I'm downloading the .SRT file from. I've used this website many times in the past to adjust.SRT files and never had problems before macOS 15.4.

The only way that I can use those.SRT files downloaded from that website is to go to the system settings privacy section and it's really annoying to have to do this every single time I download

Yes, I click "Change All" -- I'm attaching a screen recording as animated gif. Note there are 2 .srt files which have the problem -- both of which were downloaded from the website I mentioned above. When I do Get Info for file1.srt and assign it to TextEdit the problem is solved after I first use System Setting Privacy to permit it -- but importantly, this is ONLY for that file. I demonstrate this next with file2.srt, which will not open until I go through the exact same procedure.

I also tried restarting. Same thing happens again when I download an .srt file. Maybe you can go to that website and try it: https://subtitletools.com/convert-text-files-to-utf8-online/f2e824a778f9d0de

I can't upload an .srt file so here is the content of a simple one. Just paste it into a .txt file and rename it .srt

1

00:02:30,840 --> 00:02:32,439

lncredibile: sono puntuali.

2

00:02:32,759 --> 00:02:34,520

Portiamoli a festeggiare.

3

00:02:54,719 --> 00:02:56,840

Mamma!

Instead of double clicking the file, try control-clicking and choosing Open. It should give you a similar warning but include an Open button. Once a file is open this way it should work with double clicking afterwards (but you may need to do this once for each file that is problematic).

FWIW, I don't know why you would get that message. I have 800 MP4s and have never had that warning when I double-clicked the files with Sequoia 15.3.1. They open in VLC, QuickTime Player, and IINA. Mine go back to at least 2015.

I'm working as a film/media producer for exhibitions at a museum, so to me time is literary money. I switched from PC to Mac a couple of months ago to get away from all these time consuming fixes and workarounds so I can spend less time trying to make things work and more time doing the things I actually get paid for.

So I can open VLC and open an mp4 file from VLC, but if I try to open it in VLC using the mp4 file drop down menu the very same mp4 file suddenly becomes a threat that might (it just might) install malware on my Mac!?

There is no logic in that whatsoever. One month has passed by and there is still not one single sensible answer, explanation or simple working solution suggested (with apologies to the contributors on this page. I know you are trying your best to help, so keep up that good work and attitude and keep it coming :-) ). I'm starting to feel quite disappointed about the switch, and I'm starting to think you might stand a better chance with the messed up and quirked systems you know than the ones you don't.

I'm loosing money here, so...

Any suggestions? Anyone?

Sincerely yours and best wishes,

Stargazer

My experience is the same, except with .srt files instead of .mp4 -- that is, I always double click such files and they open with TextEdit, and yet all of a sudden after updating to Mac OS 15.4 I got the message mentioned in the original post. It made me wonder if that particular .srt (which I had just downloaded) was a malware problem, so I tried another .srt and had same problem. Eventually, I went ahead and used the "open anyway" feature (which I was nervous doing) and reassigned .srt files to TextEdit and now have no more problems. The downloaded .srt looked fine to me, but how would I know?

I can see Apple is trying to protect me here but I couldn't make sense of .srt files not opening when I'd always opened them before. Also, I thought Apple was supposed be immune from malware because of sandboxing of the System.

What's a person to do in that situation? Do I need malware software now?

Yes, I did that; that's what I meant by "reassigned .srt files to TextEdit"

Sure, I can double click on.SRT files now without a problem, but as I said in my post, that's not my point. 

I'm trying to support the original post, and it seems to me that the likely explanation is that recent updates of Mac OS are disassociating extensions from applications