The only time I have had a USB stick that was writable suddenly not be was when I used it on Windows 7 and somehow it became part of the machine’s Homegroup and I either clicked on the drive’s option to make it Read Only or that was a Windows 7 default. Once I changed the Sharing setting the stick was writable again.
The problem was not the stick’s fault, it was a pc, or noobie’s, fault.
However, there are other things that can protect a USB stick’s files. A business’s/university’s/school’s security settings. A machine’s user settings. A machine’s AV or other app’s security settings. Some of these things can be circumvented by booting the machine to Safe Mode.
