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I have a Samsung Galaxy S3 with a broken screen. The screen does not respond to any touch and does not display anything at all, it is black at all times. CyanogenMod 11 is installed on the device.

I need to securely wipe the device, but I've been having a very difficult time doing so, as CyanogenMod doesn't allow ADB to connect without user input, which in this case is impossible. I've done a factory reset on the phone, but didn't wipe the user data on the internal storage (not an external SD card, rather the "internal SD card" which is hosted on the main phone ROM).

How can I securely wipe the phone and delete all data left on the internal storage? I'd like to zero-out the filesystem, but still have a semi-working phone that will at least boot into Android for occasional tinkering over adb.

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If you did a factory reset, you should be able to connect it to the computer and it should allow you to delete files from the internal storage. MTP is limiting though in the fact that you can't use a secure erase program (one that overwrites the file multiple times with random data). This will be quite difficult to do with a broken screen.

The other option is to use Odin to restore it to stock. Odin overwrites all the partitions including the full /data partition which will wipe the internal storage. Just follow any of the guides on how to return to stock or unbrick the device, like this one for the international S3. If you have one of the LTE or carrier versions you will need an appropriate guide for that version. You can do everything blind in Odin, just follow the directions carefully.

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Simply boot your phone to Fastboot and issue "fastboot erase userdata". This will not really wipe the data, but without huge efforts (modifying the eMMC controller) you will get just zeros when you dump the partition. Be sure to erase cache as well.

If you run Cyanogenmod chances are you have a recovery installed that enables adb by default. Try booting your phone to recovery and connecting then with adb. From there you get a shell and can use i.e. dd to wipe the data.

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