Which method of permanently destroying data ensures that even if it is recovered, it remains unusable?

Data encryption does not permanently destroy data; it merely makes it unreadable without the appropriate decryption key. In situations where data needs to be rendered completely unusable—so that even if it is recovered, it remains inaccessible—physical destruction is the most effective method. This involves physically destroying the storage medium where the data is located, such as shredding a hard drive or incinerating a disk.

Physical destruction ensures that the data cannot be reconstructed or retrieved, unlike methods such as file deletion, data encryption, or formatting, which either make data temporarily inaccessible or do not remove the underlying data from the storage device. For instance, although formatting may remove file system references to the data, the original data could still be recoverable using specialized software. Similarly, file deletion typically just marks the data space as available for new data without overwriting the old data. Therefore, physical destruction is the definitive method of ensuring that data is permanently and irrevocably destroyed.