Implementing application whitelisting is the best strategy because it allows only pre-approved software to run on systems, thereby reducing the risk of malware infections from unauthorized applications. Regularly updating antivirus definitions is important, but it is a reactive approach rather than proactive. Disabling unneeded services can reduce the attack surface but may not directly prevent malware from running. Finally, enforcing strong password policies is crucial for overall security, but it does not specifically target the defense against malware.