Most reliable WordPress plugins for improving the security of your website is iThemes Security. This plugin offers complete defense against hacking attempts, brute force attacks, and malware infestations with a variety of capabilities like malware detection, firewall protection, and database security. 
Key Features of iThemes Security:1. Login SecurityBy lowering the chance of unwanted access, protect your WordPress login with features like two-factor authentication, CAPTCHA, and login lockdowns following unsuccessful attempts.2. File Integrity Monitoringcontinuously checks the files on your website for unauthorized changes, guaranteeing prompt detection and fixing of any possible security flaws.3. Advanced Firewall Ruleskeeps your website safe from outside attacks by filtering harmful traffic, banning suspicious IP addresses, and stopping SQL injections.4. Database SecurityProvides tools for backing up and restoring your WordPress database, guaranteeing that important data is safeguarded and recoverable in the event of a data loss or assault.5. Security Scanning and Reportsidentifies vulnerabilities through routine security scans and offers comprehensive reports to assist you in taking preventative action to strengthen your website.