A method for operating a memory system includes: performing a read operation in response to a first tag; performing a read operation in response to a second tag; performing a defense code operation corresponding to the first tag; performing an error correction code (ECC) operation on data output through the defense code operation corresponding to the first tag; and performing a defense code operation corresponding to the second tag, wherein the read operation in response to the second tag is started before the ECC operation corresponding to the first tag is completed, and wherein the defense code operation corresponding to the second tag is performed using a result of the defense code operation corresponding to the first tag.