Klez virus
When the Klez virus infects a computer, it is capable of resending itself and using any address in the infected computer's address book as the "from" address. Someone with a lot of well-known advantage players in their address book has been infected.
I have gotten ones that appeared to be from bj21.com, rge21.com, as well as several well-known posters on these boards. None were actually from the address in the "from" line.
I have gotten a few irate e-mails myself from people accusing me of sending them a virus. Since I use a non-windows system for all my e-mail, it is not possible that it came from my computer.
The easiest way to spot these is the size - usually around 130 KB, much larger than the typical e-mail. There is usually little or no text in the message.
If you look at the message path (click on "display all headers") you can usually see that it did not originate from the "from" address.
But if you're going to play around with one of these, be careful! Probably best just to delete it.
Never open any attachment, even if it appears to be from someone you know, unless you have specifically asked that person to send you something.