We are seeing a large amount of activity today (May 3rd) with this particular virus. It is being distributed via e-mail, encased in a ZIP file. The virus is travelling in a ZIP file to allow itself to make it through virus scanning software, and the text of the message encourages the recipient to open the ZIP file, thus infecting their PC. More info at this link: http://www.trendmicro.com/vinfo/virusencyclo/default5.asp?VName=WORM_SOBER.S