What CAN you do? You can destroy it, kiss your money for it good-bye and purchase another drive, or you can return it to SanDisk for a warranty replacement. Those are your only 2 options.
Contact SanDisk, explain your security concerns and see if they have a plan to protect your data. I believe I remember someone who had this issue and they authorized him to physically destroy the drive (to prevent the data from being compromised) and ship back the pieces.