A computer system having at least first and second documents, a plurality of decryption keys, and a plurality of data segments stored therein is provided. Each of the plurality of data segments is decryptable by a selected one of the decryption keys. The decryption keys include a first set of decryption keys associated with the first document and not associated with the second document, a second set of decryption keys associated with the second document and not associated with the first document, and a third set of decryption keys associated with the first document and the second document. The first document is deleted, and in response, the first set of decryption keys is rendered unusable, and the second set of decryption keys and the third set of decryption keys are not rendered unusable.