>I feel this is a bit like popping your hood at the car shop, but taking your key with you.

Do you leave all your valuables in the car when you drop it off at the shop? Or do you take them out first?

For once I think a car analogy is actually useful. But, in this analogy, "taking all your valuables out of the car" would be like removing all the important documents from the computer. Which would be a reasonable thing to do, I guess, if the computer shop really needed access to do the repairs that they need to do.

Another possibility -- maybe the computer is so borked that you can't even log on to remove your important documents. This seems more like calling somebody because your key broke in the lock... which... I guess most people would stick around? It is a little bit of a mismatch, because it is a quick fix and it isn't like you can go anywhere anyway.

Also, people from the general public don't know how to write random bits to a drive. Deleting files doesn't actually wipe the information, it just marks the space as available on the OS. Repair agents could still take an image of the drive and recover many of those secret documents.

It should be standard procedure in the repair world to hand the hard drive to the user to take home and keep only the PC for servicing.

Be aware that this can be completely different between HDDs ("spinning rust") and SSDs. HDDs don't get data cleared until it's explicitly overwritten, SSDs with OSes that support TRIM shouldn't have a lot of stray data left behind.

Also when wiping SSDs get something like Parted Magic (since at least 2018 likely earlier) that can properly erase SSDs. DBAN is NOT appropriate for SSDs in any way - extra wear from the writes, and wear leveling means you have zero idea where they're actually going.

Well, the protection strategy for my valuables is not "leave the car locked in the shop". And then there's that one customer who's "rattle" is something in the glove compartment, to extend the metaphor further.

So, in keeping with my points above, I would probably move the really valuable stuff out, but for some customers taking everything out will prevent the technician from removing the issue (and they will probably be blamed for it) and if I feel the need to completely get everything saved out of the car beforehand, I would not trust that shop with my car, either.

Let's not water the analogy down so far that it loses all connections to the current case.

I doubt anyone would leave an album with their nude pictures in the car hoping that the mechanic wouldn't do anything with it. Like...posting it all over the block where the customer lives.

This. Protecting data is practical for those of us sufficiently technically literate, but I've helped a fair number of people over the years that certainly would not be capable of doing it. (Admittedly, selection bias--the people who are asking for software help aren't the most technically knowledgeable.)

They can do this from a guest account.

Full disk encryption will protect your data.

No, it won't. They could simply put in a different BIOS chip, which records you password the next time you enter it. Or a malicious RAM chip that injects a virus at runtime and extract your data that way. Or a bugged keyboard that transmits your key presses, combined with a full copy of your disk ...

Sure, it's a bit more sophisticated than Ctrl+C/Ctrl+V. But if you're running a computer repair shop, it is quite likely that you have a good amount of technical knowledge. If someone has hardware access, you can usually see your device as compromised - especially if they have a lot of time and are expected to open up the device.

If that's your threat model, you should not be using any repair shop. And the attacks you describe are not just "a bit more sophisticated than Ctrl+C/Ctrl+V", they're most likely far beyond the abilities of most repair technicians.

> If that's your threat model, you should not be using any repair shop.

That's exactly what I said in my first comment:

>> If you really don't trust them, you probably should not give them your device at all.

> And the attacks you describe are not just "a bit more sophisticated than Ctrl+C/Ctrl+V", they're most likely far beyond the abilities of most repair technicians.

The RAM one, yes. ROM chip swaps, on the other hand, are rather common. You will need to be able to solder quite well, but given the current state of macs, this is basically a given for anyone doing repairs on them. You'd of course need to get a malicious ROM chip, which might not be so easy, but probably doable - the technician only needs to be able to swap it, not to manufacture one.

And if you can't get your hands on one - your can order a keylogger right now, for just a few bucks! [0] This was just the first result; if you invest a bit more time, you can surely find a smaller one or more fitting one. The keyboard is probably connected with USB [1], so no trouble there. As a bonus, you get all the passwords of accounts that were not saved at the time.

Sure, simply unlocking is a bit easier. But it's not like this stuff is beyond anyone who is able to debug and solder on a Mac.

[0] https://de.aliexpress.com/item/1005001988834597.html?

[1] It's in my laptops; I don't know the specifics for macs, but I doubt is something more sophisticated than a strange plug.

There are levels of trust.

"Trust not to source and install malicious hardware in order to potentially steal unknown to them data" is a magnitude apart from "Trust not to go snooping around through unprotected photo albums."