@redstarfish @cobra Depending on the kind of rootkit infestation, if you are using a proprietary OS vulnerable to rootkits, removing the HDD, putting in a new one and reinstalling will likely end in a rootkit installation again.

Some rootkits embed themselves into the BIOS or UEFI image and then re-infect a reinstalled OS (UEFI actually made security worse, as with BIOS's, such rootkits needed to be tailored per-computer or at least per-vendor, while with UEFI, you can make a single exploit jpeg with a rootkit inside that will hijack most UEFI implementations, even across architectures).