Check this nasty thing out https://www.pcmag.com/news/364046/russian-hackers-use-malware-that-can-survive-os-reinstalls

I recommend getting Malwarebytes Anti-Rootkit. It's in beta right now, but it's super useful.
Remember, when scanning for viruses, make sure your anti-virus is up to date.
Also, Disconnect from the internet before your scan. A lot of viruses can "dial home" for instructions on how to thwart your anti-virus software, and this stops them from being able to do so.

Malwarebytes: https://www.malwarebytes.com/antirootkit/

This program is super easy to use, and user friendly. It has daily updates, and it's free.

Have a safe day everyone! <3.