I doubt the any "normal" CDRW file burning will physically delete or overwrite an existing file on a CDRW. At best, writing a new version of the file with will create new catalog entries and write the new file on an untouched part of the disk. I'd expect the original version to remain untouched and likely accessible with software designed for reading such files.
I expect there's software that CAN overburn an old file. But it's probably easier to put the CD into a shredder and burn a new disk.
Of course, if it's a re-writeable disk, you can reformat the disk. That seems to take forever, so I suspect it zeroes out the entire disk.
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Last edited by RebateMonger; 03-02-2010 at 07:15 PM.