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

Copying system files from another system is unreliable because the rootkit may have infected other components beyond just system files, and manual file replacement rarely achieves a fully clean state.

A trap and trace is a network monitoring or legal investigation technique used to identify an attacker's source, not a method to remediate an already-installed rootkit.

Manually deleting rootkit files is ineffective because rootkits actively hide themselves from the file system, making it impossible to confirm all components have been removed.

Reloading from a previous backup is unreliable because the backup may have been created after the rootkit was installed, meaning the infection would be restored along with the system.

Rootkits can hook into the kernel and modify system binaries, meaning any cleanup attempt on a running or previously backed-up system may miss hidden components. Reloading from known good media (such as original installation media or a verified clean image) guarantees the OS and system files are uncompromised. This is the only method that definitively removes all rootkit artifacts rather than trying to find and delete individual components.