Hashes are cryptographic algorithms that transform input data into a fixed-size string of characters, which is typically a hexadecimal number. Common hash functions include MD5, SHA-1, and SHA-256, each varying in complexity and security. While hashes are used for data integrity verification, some, like MD5 and SHA-1, have known vulnerabilities that limit their effectiveness in cryptographic applications. The SHA-2 family and Bcrypt are more secure alternatives, designed to withstand modern cryptographic attacks.