secure erase - How do I wipe a microSD card that I can't write to?

I have a microSD card that has become read-only. I cannot write to it, or delete files from it, or format it, or repartition it. (Various computers think they can delete files, but after removing and reinserting the card, they are back).

SanDisk have offered to RMA the device under warranty, but I am concerned about sending it back with my data still on it. Is there any way I can wipe the card at a physical level without damaging it (voiding the warranty).

I guess a strong magnet is out of the question as flash isn't magnetic storage.

Edit: Clarified that this is a microSD card. It has no write-protect switch. I have also tried using dd - no result; the command hangs awaiting I/O. I have also tried using a different card reader and a different host computer (one Windows 7, the other Ubuntu) - and also without a card reader by trying to format the card while in my Android phone. The card is definitely broken.

Update: I explained the situation to SanDisk and they offered to let me return the card broken into pieces. Turns out microSD cards have about the same breaking strength as a hard matchstick.

Answer

You may consider following the legal route instead of the technological route. Probably the company in question has some sort of privacy statement - check it out on their website and get a written conformation (email with a person's name and function should be enough) that your data will be kept private. After that, send your microSD card, with a note physically attached to it stating that you explicitly exercise your right that your data is being handled according to the privacy statement.

Another option is to explain your concern to the manufacturer and agree (with the manufacturer) to the following route (before execution of it): make a picture of your microSD card, showing that it is in perfect physical condition. Take a picture of today's newspaper with it to date it. Print a log of your failed deletion of the file - preferably dated after you took the picture of the card. After that, take a hammer and smash a nail through your microSD card and send it all (photo, print and destroyed card) back to the manufacturer.

Finally, if you're not willing to take the risk, take your losses and buy a new one. For compensation you might want to consider buying a lottery ticket too and try your luck there. :-)