I didn't send it, you idiots! Configuring e-mail servers to scan for viruses is a good thing. But these days, the one place you can be virtually certain it didn't come from is the person whose e-mail address is in the From line.
If you run a mail server, please set up virus scanning. If your mail server does virus scanning, please make sure it doesn't send these nuisance e-mails to the forged From address.