Infected PC: How can you reformat and reinstall Windows without the infection spreading via the installation media?

Question

Despite extensive internet research, I have not seen anyone answer this question. I'm definitely no computer expert so maybe I'm just missing something but...here goes.

Say my computer is infected and I want to be absolutely positive I've removed the malware. So, I decide to reformat all internal drive partitions and reinstall Windows completely, using an SD card I created when I first got the computer as installation media.

How can this be done without the virus potentially (automatically) transferring to, and then returning from the installation media itself?

Every guide I've read instructs that the reformatting be accomplished via the new installation media (e.g. using Windows Setup). This does make sense to me, because I suppose you can't format using only the internal hard drive, being as all the software there will be wiped out, leaving nothing left to "do" the formatting.

But here's what I don't get: being as the installation media will thus necessarily be inserted prior to formatting, couldn't the virus immediately spread automatically from the computer to the installation media, and then spread right back to the computer after formatting, thus making reformatting useless for removing automatically spreading viruses?! I thought reformatting was a guaranteed last resort.

Answer 1

Create the installation media yourself: Download the legitimate Windows (from Microsoft Directly) ISO to a second computer, and use the provided legitimate Windows Bootable USB tool (Also provided by Microsoft). Using a second, completely virus free computer mitigates the risk of anything corrupting your new media.

If you'd like to recover information from your old drive - you could take that drive out and attach it to a second system - gather documents you want, which does have a risk attached to it, and then format the disk on the second PC before installing a new copy of Windows on it.

Answer 2

I don't intend to nag, but backdoored installation media is quite common. Wipe your entire system and use a * cough * genuine version after verifying the file signatures.

Answer 3

The way I usually do it is by using Hiren's Boot CD. Boot from the usb it is on and then start Mini XP. That way you have a clean windows install from which you can start formatting your HDD.