What is the BEST alternative if you discover that a rootkit has been installed on one of your computers?

A.
Copy the system files from a known good system

B.
Perform a trap and trace

C.
Delete the files and try to determine the source

D.
Reload from a previous backup

E.
Reload from known good media

Explanation:
If a rootkit is discovered, you will need to reload from known good media. This typically means performing a complete reinstall.