1. Sanitize user input: Any data received from the user should be sanitized and validated before being used in the application. This helps prevent SQL injection, cross-site scripting (XSS), and other exploit attacks.

2. Use parameterized queries: Instead of passing raw user input directly into database queries, use parameterized queries or prepared statements. This helps prevent SQL injection attacks by automatically escaping special characters.

3. Protect against cross-site scripting (XSS): Use output encoding or escaping when displaying user-generated content to prevent XSS attacks. This can be done using functions like htmlentities() or htmlspecialchars().

4. Implement role-based access control: Assign different levels of access to different users based on their roles. This can help prevent unauthorized access to sensitive data or functionality.

5. Secure session management: Use secure session management techniques such as session hijacking prevention, session expiration, and creating a secure session ID.

6. Use strong password hashing: Hash passwords using a strong algorithm like bcrypt or Argon2 instead of simple MD5 or SHA1 hashing. This helps protect user passwords in case of a data breach.

7. Implement account lockouts: Implement mechanisms that lock user accounts after a certain number of failed login attempts. This helps prevent brute-force attacks on user accounts.

8. Keep software up to date: Regularly update your PHP version and other software components to ensure you have the latest security patches. This helps protect against known vulnerabilities.

9. Use HTTPS: Use HTTPS instead of HTTP to ensure secure communication between the client and the server. This helps prevent data interception and tampering.

10. Implement secure file uploads: Validate and sanitize file uploads to prevent malicious files from being uploaded to the server. Also, store uploaded files outside of the web root directory to prevent direct access.

11. Limit error reporting: Disable or limit error reporting to avoid leaking sensitive information to potential attackers. Set the display_errors directive in php.ini to “Off” or log errors instead of displaying them on the screen.

12. Use a web application firewall (WAF): Install a WAF to help protect against common web application vulnerabilities and attacks. A WAF can help block malicious requests and provide an extra layer of security.

13. Regularly scan for vulnerabilities: Use vulnerability scanning tools or services to regularly scan your PHP applications for potential vulnerabilities. This can help identify and fix security issues before they are exploited.