I have a Mifare UltraLight NTAG216 (NFC Forum Type 2).
It is not password protected, but the Android app NXP TagInfo says:
NFC data set access: Read-Only
NDEF access: Read-Only
E1 10 6D 0F
Looking at the memory dump from NXP TagInfo:
[E2] . 00 00 00 BD (LOCK2-LOCK4, CHK)
[E3] . 04 00 00 FF (CFG, MIRROR, AUTH0)
HOWEVER, the NXP TagWriter app allows me to format the tag, which successfully removed all data (I verified before and after). I can also repeat the formatting (both Erase, Quick Format, and Format all).
But any write attempts fail with a "read only" message.
How can I determine if this write protection is permanent, and if not, remove it?
According to a related question, it might have to do with the configuration pages, which can be both temporarily and permanently protected. But I'm not sure what that means.
SOLVED: After restarting my android device and formatting the tag once again, I could again successfully write to the tag.
Curiously, it still reports Read-Only as described below. I guess that's normal (perhaps for this particular chip) and it was just an intermittent problem.