Some of malware that’s called Virus can inject itself into executable file.
Such as Win32.Virut , Win32.Alman , Win32.Fujack , Win32.Hala , Win32.Sality or Win32.Parite
It’s infect an exe files by modification an original file.
Back to a thread topic, I’m suggest Can the infected files repair by Comodo Antivirus ?
Because some AntiVirus software can’t do that it’s clean by deleting file.