Which option is a method for malicious code to spread?

E-mail attachments serve as a common method for malicious code to spread because they can easily be shared and opened by users who may not be aware of the potential threat. When a user receives an e-mail with an attachment that contains malware, simply opening that attachment can result in the execution of the malicious code. This type of distribution exploits human behavior, as users often trust emails from familiar contacts and may inadvertently allow harmful software to install itself on their system.

In contrast, antivirus software is designed to detect and eliminate malicious code, making it a protective measure rather than a vector for spreading malware. Document scanning is typically a security protocol that checks files for malware before they are accessed or run, thereby reducing the likelihood of infection. Firewall settings act as a barrier to prevent unauthorized access and can help block malicious traffic, which ultimately fortifies security rather than facilitating the spread of harmful software.