Correct Option: C (II, III, and IV only) Explanation of the Correct Answer To understand why option C is the correct answer, we need to analyze each symptom listed in the question and determine whether it is indicative of a computer virus attack.

1. I. Improved processing speeds:
2. This symptom is not typically associated with a computer virus. In fact, a virus usually degrades system performance by consuming resources, causing slowdowns, or leading to erratic behavior. Therefore, this symptom does not indicate a virus attack.
3. II. Drive light coming up without apparent reason:
4. This symptom can indicate a virus or malware activity. If the drive light is active without any user action (like opening files or running programs), it may suggest that a virus is accessing files or performing operations in the background. This is a common sign of malicious software.
5. III. Unexplainable printer activity:
6. This symptom can also be a sign of a virus. If a printer is producing documents or print jobs that the user did not initiate, it could indicate that a virus is attempting to print out information or is executing commands without the user's consent.
7. IV. The disappearance or strange files appearing on the screen:
8. This symptom is a classic indicator of a virus. Viruses can delete files, corrupt data, or create new files that are often strange or unexpected. Users may find files that they did not create or notice that important files have vanished, which is a clear sign of malicious activity.

Given this analysis, we can conclude that symptoms II, III, and IV are indeed indicative of a computer virus attack, while symptom I is not. Explanation of Why Other Options Are Incorrect

• Option A (I, II, and III only): This option includes symptom I, which we established is not a sign of a virus. Therefore, this option is incorrect.
• Option B (I, III, and IV only): Similar to option A, this option also includes symptom I, which is not associated with a virus. Thus, it is also incorrect.
• Option D (I, II, III, and IV): This option includes all symptoms, including symptom I, which we have determined is not a sign of a virus. Therefore, this option is incorrect as well.

Summary of Key Points

• Correct Answer: C (II, III, and IV only).
• Symptoms II, III, and IV are indicative of a virus attack, while symptom I is not.
• A virus typically degrades system performance rather than improving it.
• Unexplained drive activity, printer activity, and strange file behavior are common signs of malware.

Revision Summary

• A virus usually slows down a computer, not speeds it up.
• Unexplained drive activity can indicate background malicious processes.
• Unexplainable printer activity may suggest unauthorized print jobs due to a virus.
• Strange file behavior (disappearance or appearance) is a classic sign of virus activity.