That's a lot and sorry for your loss.
It's not really a good storage to keep your money on a metamask. A small amount would do but having that sums of money, it should have been into a hardware wallet. You should have swapped it into actual btc and not wrapped so that you'll be forced to keep it onto a hardware wallet.
The cause might be that software you've downloaded prior to the hack and whether you use mac os or windows, there has been a lot of hijackers in different app marketplaces.
I think, it is not the metamask itself that failed the security here.
The OP mentioned about installing a software application and at the same time expiring his norton security subscription.
So that case, he was very vulnerable to outside attacks. And how did hackers know about his large crypto funds?
It may be someone that knew him from social media channels, and that they knew he is into crypto with good amount of coins.
Because we don't know the whole story, the hackers may know the OP for all we know.
So aside from securing your funds in your own hardware wallet, make sure you don't disclose your crypto activities in social media.
What I've said about metamask is that it's not really a cool place to store your funds for long. I did mentioned that the cause might be the software that he has downloaded.
It could have been a spyware or malware that was able to penetrated the system and we don't know how they do that but that's where they are expert for, in stealing other people's money.