More Information thanks to Trillian Forums

Email spoofing
W32.Sobig.F@mm uses a technique known as “spoofing,” by which the worm randomly selects an address it finds on an infected computer. The worm uses this address as the “From” address when it performs its mass-mailing routine. Numerous cases have been reported in which users of uninfected computers received complaints that they sent an infected message to another individual. For example, Linda Anderson is using a computer infected with W32.Sobig.F@mm. Linda is neither using an antivirus program nor has the current virus definitions. When W32.Sobig.F@mm performs its email routine, it finds the email address of Harold Logan. The worm inserts Harold’s email address into the “From” portion of an infected message, which it then sends to Janet Bishop. Then, Janet contacts Harold and complains that he sent her an infected message; however, when Harold scans his computer, Norton AntiVirus does not find anything, because his computer is not infected. So the question it: WHICH ONE OF YOU SCATTER BRAINS IS INFECTED WITH THIS WORM!!?? GET IT CLEAN BECAUSE I’M SICK OF GETTING EMAIL FROM ALL THESE PORN SITES SAYING I’VE SENT THEM A VIRUS!!!!!!!!!!!!

Please search your Windows folders for these files: WINPPR32.EXE WINSTT32.DAT
If you have them, you are the one infected, and I can help you clear it.
Or you can try to clear it yourself with this easy utility.