There is a new e-mail virus: W32.Sobig.F@mm discovered on the 18th of august, 2003.
The virus sends e-mails using fake e-mail addresses, for example mine: parhuzamos@yahoo.com
From Symantec - W32.Sobig.F@mm (http://securityresponse.symantec.com/avcenter/venc/data/w32.sobig.f@mm.html):
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.
I'M NOT SENDING THOSE E-MAILS, THE VIRUS DOES. MY COMPUTER DOES NOT HAVE THE VIRUS. I'm using Yahoo! Mail only, so there is no way that I could send an e-mail message without knowing it.