Scanning your system is a necessary task. But, there are other tasks which are necessary while scanning your PC. This Techvedic tutorial outlines the privacy policy related with scan, what to do if Windows running on your PC can't complete the scan as well as additional information to keep up PC health.
Is your computer infected with a virus that is preventing you from downloading security updates from the Internet or from running any antivirus program on that machine? Or are your looking for an antivirus software that can be carried on a USB drive to quickly scan any disconnected computer(s) for viruses or malware?