I have download a supposedly 'untouched' version of msdn ISO of windows 8.1 all versions 64 bit, but after checking the SHA-1 number of the ISO against the MSDN website, I realize that the ISO has in fact been tapered with. Even so, I have extracted the WIM file and scannned it thoroughly aswell as all the remaining files using an anti virus software and it could not find any malware or viruses. So would it be safe to say that the ISO is not contaminated and is safe to use or is there malware and viruses hidden so deeply that a virus checker cannot find it. If so, how is that possible? Cheers!