An attacker starts their attack by using open$-$source intelligence to identify a target. They then use a spear$-$phishing email with a malicious link enticing the recipient to click on it$.$ The user is curious and visits the site, where they are prompted for a username and password. The user enters the credentials, which are promptly sent to the attacker, who uses them to gain access to the organization's network.

Which of the following could have prevented this attack?

A

Strict firewall rules

B

Strict spam filters

C

User education

D

Antivirus