The Palo Alto Networks source describes HNDL as a present-day threat: attackers can collect or steal encrypted data now and store it until future quantum computers may be able to decrypt it. In other words, the risk starts when the data is intercepted or copied, not when quantum computers finally arrive.[1][2]
This makes HNDL especially relevant for data that must remain confidential for a long time, because the value of the stolen ciphertext can persist for years or decades before a decryption attempt is possible.[3]
HNDL is difficult to detect and reverse because once encrypted data has been collected, organizations cannot easily "unharvest" it; they can only reduce future exposure by migrating systems and data protection strategies before quantum decryption becomes practical.[7][8]
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