DES (Data Encryption Standard) is a symmetric block cipher that uses a 56-bit key to encrypt and decrypt 64-bit blocks of data. It was developed by IBM in 1975 and adopted by the US government as a standard for encryption. However, DES has been proven to be insecure and vulnerable to various attacks, such as brute force, differential cryptanalysis, and linear cryptanalysis. A brute force attack can break DES in a matter of hours using modern hardware. Differential cryptanalysis can reduce the number of keys to be searched by a factor of four, and linear cryptanalysis can reduce it by a factor of two. Therefore, DES is the least secure encryption algorithm among the options given.

References: Types of Encryption, Secure Organization’s Data With These Encryption Algorithms, Comparative study of symmetric cryptographic algorithms