best way to remove malware from an infected PC?
My reasoning is: once an infected computer has booted, the malware is
already running. That malware may prevent the installation of anti-
malware software. Or, it may prevent anti-malware software from
updating, or otherwise running correctly. Or it may re-spawn itself, or pull new viruses from the internet.
On the other hand, if the malware has disguised itself as legitimate
windows system files, then if you from an external drive, the software
on that external drive may not recognize the disguised malware.