Researchers have discovered a new low-level machine language attack that can be hidden in the firmware that controls disk operations.

http://www.geek.com/apps/nsa-malware-found-hiding-in-hard-drives-for-almost-20-years-1615949/

Someone out there figured out how to hide persistent, invisible espionage malware inside the firmware of your hard drives. Now it’s been discovered that they’ve been using it to spy on targets for nearly 20 years. This particular piece of malware is delivered via modified hard drive firmware, and Kaspersky says that it’s compatible with nearly all major hard drive brands: Seagate, Western Digital, Samsung, you name it. Once it’s there, it’s nearly impossible to get rid of or even detect. Since it’s not taking up space on the hard drive’s platters, it can easily re-infect a system even after a drive has been fully formatted.