One of the most dangerous yet common mistakes is the inclusion of hard-coded credentials (e.g., usernames, passwords, API keys) directly in source code. If such code is leaked, stolen, or pushed to a public repository, attackers gain immediate access to sensitive systems. Secure coding practices demand removing hard-coded credentials and instead storing them securely in configuration files, environment variables, or dedicated secrets management systems. This not only reduces the risk of credential leaks but also makes key rotation and credential lifecycle management easier.