What is a major security feature introduced in Windows XP?

The major security feature introduced in Windows XP is user account control. This feature was implemented to enhance security by allowing users to operate with limited privileges and requiring elevated permissions for administrative tasks. This significantly reduces the risk of unauthorized changes to the system and protects against malware that may try to exploit administrative access.

While digital certificates, firewalls, and antivirus software play important roles in security, they were not the most notable new components introduced with Windows XP. Digital certificates are primarily used for verifying identities and securing communications, which existed prior to Windows XP. Firewalls were also available in earlier versions of Windows in some form, and antivirus software integration was not a native feature of the operating system itself. User account control represented a fundamental shift in how users interacted with their systems and how security was managed, making it a standout feature of Windows XP.