Do you trust your hardware?
Do you believe that your hard drive does not contain malware? I mean not what you maybe think.
Malware can be installed on the hard drive's microcomputer. All hard drives contain another computer inside them - with his own processor, RAM, flash memory, etc. This computer have access to the main computer's RAM.
Also your BIOS/UEFI may contain malware.
Also your CPU contains entire computer (like hard drives). Search for "intel amt rootkit" for more info.Rootkit in your laptop: Hidden code in your chipset and how to discover what exactly it does [PDF]
All anti-virus programs can not access and verify the memory of these separate computers, hidden inside your computer.
Key phrases you may want to type into Google:
hard drive firmware rootkit NSA hard drive firmware Intel AMT rootkit Intel ME rootkit BIOS UEFI malware BIOS UEFI rootkit
Here is somewhat safe alternative, but this does not solve the problem with the CPU and the hard drives:
Here is a proof of concept malware for hard drives: http://spritesmods.com/?art=hddhack