Final Answer:
If you receive an email with a classified attachment while working on your unclassified system, you should promptly report the incident to your organization's security or IT department and refrain from accessing the attachment until the appropriate security measures are taken. Option C: "Report the incident to your security or IT department and refrain from accessing the attachment" is the recommended course of action.
Step-by-step explanation:
Handling classified information requires strict adherence to security protocols. In the given scenario, it is crucial to prioritize security and follow established procedures. By reporting the incident to the security or IT department, you enable them to assess and mitigate potential risks. Accessing the classified attachment on an unclassified system poses a security threat, and refraining from doing so helps prevent unauthorized disclosure of sensitive information. This course of action aligns with best practices for information security.