DES (Data Encryption Standard) is considered the least secured among the given options. It uses a smaller key size of 56 bits, which makes it vulnerable to brute-force attacks. Modern encryption standards like AES-128 and AES-256 offer a much higher level of security. 3DES, although designed to improve upon the security of DES by applying the DES algorithm three times with different keys, is still not as secure as AES. Therefore, DES is the least secure encryption algorithm listed here.