If the boot camp partition of my mac gets a virus, will the macOS part be safe? If the macOS part gets a virus, will the Windows part be affected?


Yes in general - Bootcamp doesn’t lock down the files on either side so you are at risk for data exfiltration / modification / deletion on both sides if either OS is compromised by a competently designed malicious program.

Some virus are simplistic or bug ridden so you might get lucky, but I would protect the Mac side with FileVault if you can’t realistically secure windows. Same on the Mac side - encrypt windows yo be safe.

You could also choose virtualization solution where you could lock things down better with some research and training.

  • I don't use boot camp so I am not too sure but is SIP enabled in Windows? Could malware theoretically load something into the boot sequence/EFI partition so that when FileVault is decrypted the file will automatically be transferred over? Or even worse interact with the kernel? – JBis Sep 2 '18 at 12:16
  • @JBis no - SIP handcuffs macOS only - booting to an alternate OS gets by that protection. EFI is not protected fully - the T2 chip in the iMac Pro and latest MacBook Pro can verify that the core OS is cryptographically signed and protected. Apple has started to protect against this, but the support is starting to ship - not a done deal in fall 2018 – bmike Sep 2 '18 at 20:12
  • Hmm interesting. A bit off topic but will these T2 chips prevent one from altering the EFI partition. I use it to install refine and others. – JBis Sep 2 '18 at 20:28
  • @JBis I think the design goal is to prevent booting - alert that tampering is detected as opposed to stopping the modification. I haven’t seen this reverse engineered or poured over the documentation yet tbh. – bmike Sep 2 '18 at 20:45

Most viruses (like 99.999% of them) are unable to transfer between operating systems for many different reasons, but theoretically a virus could spread between the two operating systems. What is more likely is that the virus would corrupt the partition table itself.

Take a look at the following links for more info:

Please note my percent is not based off of any legitimate statistics, it is exaggerated.

  • There are some competent nasty malware out these days. I’ll put up an answer explaining the risks due to files being easily accessible without encryption. – bmike Sep 2 '18 at 6:27

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