正解The correct answer is ア. When disposing of or transferring an HDD, data-erasure (data-wiping) software used to prevent information leakage overwrites all areas within the HDD with meaningless data (such as random numbers or fixed values), putting the original data into a state where it cannot be recovered. Simple deletion or formatting leaves the actual data behind, which a recovery tool can still read out, so ア, which overwrites all areas, is the appropriate function of the dedicated software.
×Incorrectイ
Searching all areas and setting a password on files created with office tools is merely access control for individual files. The actual data still remains on the HDD, so it does not serve as a countermeasure against information leakage at disposal (making data unrecoverable), and it is not a function of dedicated data-erasure software.
×Incorrectウ
Encrypting files that have not been deleted is a process that raises confidentiality, but the data itself continues to exist on the HDD. Since encryption is not erasure of data, room for recovery remains, and moreover the already-deleted but still-remaining areas are not covered. This differs from an erasure function intended for disposal.
×Incorrectエ
A logical format only rewrites the file management information (the file system), while the actual data remains on the sectors. Although it finishes in a short time, the original data can still be read out with a recovery tool, so it does not amount to reliable erasure as a countermeasure against information leakage.
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Principle of data-erasure (data-wiping) software: it overwrites all areas of the HDD with meaningless data so that the original data cannot be recovered. This is the basis of information-leakage countermeasures when disposing of or transferring an HDD.
With deletion or a logical format, only the file management information is cleared while the actual data remains and can be recovered. To erase it reliably, overwriting (or physical destruction) is necessary.