I was re-installing Windows for a customer that fell for a phone tech support scam (the scammer had control for quite a while). I was unable to run antivirus scans (on multiple programs, including Malwarebytes Chameleon, it said unable to scan after starting), but had no other visible solutions. After seeing the customer had little personal files or programs installed, I decided a re-install of Windows was the way to go. I started a drive wipe out of an overabundance of caution, but after seeing it would take 12 hours, decided it was not worth the time as well as the wear and tear on the drive. I re-installed Windows and gave the computer back to the customer (and scanned it both with Malwarebytes and Panda to ensure no viruses had been transferred), but have been worried of a boot sector virus that may have remained after a reformat. Is this a valid concern?