An analyst is working on an email security incident in which the target opened an...

Isolating the infected attachment is the best course of action for the analyst to take to prevent further spread of the worm. A worm is a type of malware that can self-replicate and infect other devices without human interaction. By isolating the infected attachment, the analyst can prevent the worm from spreading to other devices or networks via email, file-sharing, or other means. Isolating the infected attachment can also help the analyst to analyze the worm and determine its source, behavior, and impact. References:

https://www.security.org/antivirus/computer-worm/

https://sec.cloudapps.cisco.com/security/center/resources/worm_mitigation_whitepaper.html