These days, malicious software seems to be infecting Windows computers, encrypting their data against their will, and asking for a Bitcoin ransom in exchange for the encryption key.

  1. In order for such a software to run "successfully" on an OS X machine, would the user first have to run it and give the sudo password? Is such a threat conceivable on OS X without the user doing this?

  2. Would FileVault protect against this? Could a ransomware program, if unwittingly installed by a user (who also confirmed with the sudo password), take your FileVault data hostage? Could it take hostage also your TimeMachine backups even if they are encrypted?

  3. In general, how (in)vulnerable is OS X to encryption ransomware, and how careless/unsavvy do the actions of a user have to be in order to actually have his or hers data taken hostage?

  • In order to be effective, the ransomware will have to 'infect' the time machine backups also. Without pretending it isn't possible, it's going to need some serious effort doing that. – EDP Jan 22 '16 at 15:46

At the moment, it's relatively safe. Most ransomware has targeted Windows users, and so far, the ransomware that has targeted Macs has been relatively crude. The latest (very crude) Mac ransomware threat did not destroy Time Machine backups, but was not stopped by FileVault.

In general, the steps you describe in part 2 of your question are unlikely to help protect you; encrypted data is not harder to re-encrypt than unencrypted data.

Vulnerabilities that don't require what you describe in part 1 of your question are rare, but are found from time to time. Mac Ransomware that uses one has yet to be seen. It's likely that Mac Ransomware will slowly get more sophisticated, and careful, savvy users are unlikely to lose their data to ransomware anytime soon. But I can't predict the future. This answer may live on for years and such ransomware is likely to turn up eventually. But the meaning of "careful, savvy user" will likely change over time as well.

At present:

Ransomware will have a relatively hard time deleting or encrypting online Time Machine backups. Even as root/superuser, it's hard to delete Time Machine backups:

sudo rm /Volumes/BK1/Backups.backupdb/Orion/2017-03-18-184155/BOOT/var/du--sortedALLk.13224.bak
override rw-r--r--  root/wheel for /Volumes/BK1/Backups.backupdb/Orion/2017-03-18-184155/BOOT/var/du--sortedALLk.13224.bak? y
rm: /Volumes/BK1/Backups.backupdb/Orion/2017-03-18-184155/BOOT/var/du--sortedALLk.13224.bak: Operation not permitted

But it's far from an insurmountable problem. I think folks should assume that the additional step that the ransomware would have to go through (which I'm familiar with but choosing not to publicize - I'd rather not help script kiddies) to be able to delete or encrypt TM backups is something most Mac ransomware you're likely to become infected with will be programmed to take.

Time Machine users are encouraged to allow backups to run often, which makes them quite vulnerable to ransomware.

Therefore some backup drives should be connected less often and kept more secure - not fully accessible to the system - specifically to protect from ransomware.

Typically, victims realize they've been infected with ransomware only when the ransomware announces its presence. So it's likely you won't be able to tell that a computer is infected with ransomware before it has a chance to encrypt the data on a frequently or continuously connected external drive. Assuming otherwise is far from a safe assumption. The ransomware threat makes better disaster preparedness, including having more numerous offline physical backups, more important.


This is a tough one to answer. I have seen discussions on MacInTouch.com about just this subject. And if you keep up with news online about such tings you will find that opinions vary from "Chicken Little" to, "nah, don't worry about it on a Mac."

The truth likely lives somewhere between the two.

Generally viruses of all types have a bit of a harder time on the Mac. I run without an installed virus scanner on all my Macs. But I have been working, professionally, supporting Macs since System 6. So, with care, recent backups and an alert mind (yeah right...) you are fairly safe without a virus scanner. That said I always recommend that you have a virus scanner installed and kept updated.

Ransomware usually (like many other forms of malware on the Mac) requires that you enter a username and password to give the malware installer rights to do it's dirty work. However there are vulnerabilities on Mac O/S that supposedly don't require administrative authentication to root your computer.

There is also malware that tries to masquerade as ransomware. A co-worker recently opened a link to a video that then infected Safari on his Mac with what looked like some malicious javascript. But starting Safari in Safe mode, resetting to defaults and then a thorough cache cleaning (we used Onyx) removed the so called ransomware from his Mac. he was annoyed with himself for falling for it saying, "I knew better and never should have opened that video."

Yeah that does not fully answer your questions (parts of 1 and 3) but an online search for articles on ransomware on Macs and a search of MacInTouch, might help educate you further. Or maybe someone here has some more experience with it.

  • I know this is several months later, but: Do you know if FileVault would protect against ransomware? Would a process without root privileges be denied access to delete/modify/encrypt FileVault protected folders? Would ransomware that had been given root privileges by an unwitting user (who thought that the software was something else) be able to delete/encrypt/modify your FileVault data? – Revetahw Apr 13 '16 at 11:43
  • I have no real experience with FileVault, sorry. – Steve Chambers Apr 13 '16 at 15:21
  • Alright, I think I'll post that as a separate question. – Revetahw Apr 13 '16 at 15:22
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    @fiksdal FV protects the whole disk but is unlocked after a user has logged in. So I don't see how this protects against ransonware. – nohillside Apr 17 '17 at 6:29

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