I have been searching for quite a while for a portable antivirus program that runs on Windows PE. The antivirus patterns can't be updated, the tool can only be used for 10 days after the download, and it doesn't run on Windows PE. Safety Scanner has three major downsides. In most cases, a full scan is the best option. The customized option is useful if you already suspect that a virus has infected a certain folder. Therefore, I wouldn't use this option because an antivirus scan only makes sense if you are more or less certain afterwards that the system is clean. Quick scan searches in 'areas of the system most likely to contain viruses, spyware, and other potentially unwanted software.' It is unclear where these 'areas' are. Safety Scanner offers three scanning options: quick, full, and customized. If you don't have a Microsoft antivirus scan engine installed (Microsoft Security Essentials or Forefront), you can use the Safety Scanner if you need a second opinion. A portable antivirus program is useful whenever you want to scan a PC that lacks antivirus software.

Microsoft safety scanner cnet