Canon HF M31 - Manual (Page 185)

Additional Information
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Disposal
When you delete movies or initialize the memory, only the file allocation
table is altered and stored data is not physically erased. Take the nec-
essary precautions when you dispose of the camcorder or memory
card, for example by physically damaging it to prevent the leakage of
private data.
If giving the camcorder or memory card to another person, initialize the
built-in memory (
only) or memory card using the [Complete
Initialization] option ( 0 36). Fill it up with unimportant recordings, and
then initialize it again using the same option. This makes recovering the
original recordings very difficult.