Force an USB drive to become readonly


I have a Sandisk Cruzer Fit drive which I want to use for removing virusses on infected systems and/or installing a new OS. Because (You guessed it) I’m quite a tech guy it will meet with a lot of virus infected PC’s, but also It will meet with a lot of PC’s with other hardware or software issues. To prevent becoming a source of infection I’d like it to become readonly (and I don’t care if I have to throw it away to become readable again).

I googled it, but I’m only finding the other way around; People who have a locked up drive which is readonly and want to make it writable again. Is there any known way to push the drive into this state, because that would be perfect. Of course I understand that Sandisk no longer supports it.

I spoke to Customer Services in the Netherlands, which represensative was very quick and friendly (A+ for support), but he also could not answer this question. On asking wether sandisk had any other drives with a hardware switch he unfortunately refered me to Flash or CF, which I don’t prefer because they don’t boot in a lot of environments.

I know I can make the partition readonly, but I’m afraid virusses might know that trick.

Any and all help would be very much appreciated.

Kind regards,


I assume to clean/fix/etc other’s pc you boot your USB drive to run your AVs and etc.  If so, if you turn their pc’s off before inserting your USB drive you are safe.  The malware on the infected machines won’t be running when you insert your drive and boot it.

Hi Ed,

Thank you for your answer.

Unfortunately it is/should be multipurpose. Not the best example; If a system is slow it might be because CPU/GPU is overheating, but it might also be because of a virus. Finding out which one it is is most of the time easy, sometimes hard, sometimes extremely hard and I do need my own specialised toolset to remedy the issue. Configuring/forcing a sandisk as readonly would be the same as using a cdrom, not a chance that it will ever get infected.

I would love to hear from anyone if it is possible (because it is possible, I see the reverse behavior of sandisks when I google it) to make the drive readonly.

Hoping someone has any ideas?

Kind regards,


Until someone can determine how to break the drive so it goes read only you can still use it to repair machines. Boot it and run a AV & malware scan on the machine’s hard drive and if clean then boot the machine normally and use your drive to diagnose other problems. BTW In that AV/malware apps update frequently a broken read only USB drive quickly becomes obsolete in dealing with infections. PS There is supposedly a Registry entry that enables/disenables the Read Only attribute for a removable drive, you could try using that approach on machines your working on.