The nonk 6

ClamWin 
 
Description: ClamWin is a popular choice for portable malware scanning; it makes the top spot here mainly for lack of competition from truly portable apps! In any case, it scans for both viruses and spyware. But it won't provide real time protection, and it doesn't have scheduling or program updating in the portable version. It allows you to update the database with the newest threats any time you want (or use ClamWinPortableDBUpdate for auto updates), but dialup users will have great difficulty getting them initially, if they are patient enough to get them at all (it took me a morning while surfing around doing other stuff!). Verified TruPortable.
Be sure to upload any newly downloaded or suspicious files to an online multi-scanner such as Virustotal or Jotti before copying them to your flash drive and use ClamWin for regular scanning. Additionally, I suggest periodic scanning with your regular antivirus and antispyware software when you can. Many of the best antivirus and antispyware scanners/removers must be installed.