PHP is a popular programming language used for website development. While PHP itself may not directly handle data security, there are several best practices and techniques that PHP developers should follow to ensure the security of their applications and protect user data.

1. Input validation and sanitization: Always validate and sanitize user input to prevent malicious code injection or unexpected behavior. Use functions like `filter_input()` and `htmlspecialchars()` to sanitize input and escape special characters.

2. Prepared statements and parameterized queries: When interacting with databases, use prepared statements or parameterized queries instead of directly embedding user input in SQL queries. This helps prevent SQL injection attacks by automatically escaping special characters.

3. Password hashing: Never store passwords in plaintext. Use PHP’s built-in password hashing functions like `password_hash()` to securely hash passwords. When verifying passwords, use `password_verify()` to compare the hashed password with the user-entered password.

4. Session management: Properly manage user sessions to prevent session hijacking and session fixation attacks. Set secure session cookies with the `session_set_cookie_params()` function and regenerate session IDs after successful login using `session_regenerate_id()`.

5. Cross-Site Scripting (XSS) prevention: Use output escaping functions like `htmlspecialchars()` or output encoding techniques to prevent XSS attacks. Always be mindful of where and how data is being outputted, ensuring that user-supplied data is properly sanitized before being displayed to users.

6. Cross-Site Request Forgery (CSRF) protection: Implement CSRF protection by adding anti-CSRF tokens to each form and verifying the tokens on form submission.

7. Secure file uploads: Validate and sanitize file uploads to prevent malicious files from being uploaded to your server. Use functions like `pathinfo()` to validate file extensions and check file MIME types using the `finfo` extension.

8. Secure communication: Always use HTTPS for secure communication between the client and the server, especially when handling sensitive data. Use HTTP-only and secure flags when setting cookies to ensure they are only transmitted over secure connections.

9. Regularly update PHP and related libraries: Keep PHP and its associated libraries up to date to ensure any security vulnerabilities are patched promptly.

10. Error handling and logging: Handle errors properly to prevent sensitive information from being exposed to users. Log any critical errors or exceptions to a secure location for analysis and troubleshooting.

By following these best practices, PHP developers can enhance the security of their applications and protect user data from various security risks.