What is application whitelisting and why is it effective?

Application whitelisting, also called application allowlisting, permits only pre-approved software to execute on a system and blocks everything else by default. This is a deny-by-default approach that is fundamentally more secure than traditional antivirus, which allows everything except known malware. Whitelisting prevents zero-day malware, unauthorized software installation, and many fileless attacks because the malicious code is not on the approved list. The challenge is maintaining the whitelist as legitimate software is updated and new applications are added.