In practice, malware has numerous ways to attack files, not just writing to the filesystem itself. https://www.microsoft.com/security/blog/2018/09/27/out-of-sig

In practice, malware has numerous ways to attack files, not just writing to the filesystem itself. https://www.microsoft.com/security/blog/2018/09/27/out-of-sight-but-not-invisible-defeating-fileless-malware-with-behavior-monitoring-amsi-and-next-gen-av/ https://www.microsoft.com/security/blog/2018/09/27/out-of-si... is a good overview of some of the techniques used. Generally, you need to ensure that programs can't get other already-trusted programs to do their bidding, and that's tough. Apple has done a lot of work here, but the more you request user intervention to enable access, the more you invite a frustrated user simply clicking yes to everything, which defeats the purpose. https://tidbits.com/2018/09/10/mojaves-new-security-and-privacy-protections-face-usability-challenges/ https://tidbits.com/2018/09/10/mojaves-new-security-and-priv... is a good overview. More generally, though, for the use case of infrequently accessed personal files, a hardened mirror of your data that specifically keeps old versions of files, even if told by a corrupted system that they should be deleted or rewritten, is the type of thing you need. And systems like Dropbox are designed to do just that. If any file can be rewinded to a specific point in time at any time, is that particularly different from someone trying to answer the UX problems with permissions dialogs for filesystem access etc. by saying "if someone tries to delete/modify a file, let's just log that it happened and ensure the user can easily (in this case retroactively) prevent them from doing so?"