I just received the following email from noreply@polynode.com. For the record, polynode.com is a domain I maintain for personal use.

Dear user of Polynode.com,

Some of our clients complained about the spam (negative e-mail content)
outgoing from your e-mail account. Probably, you have been infected by
a proxy-relay trojan server. In order to keep your computer safe,
follow the instructions.

For further details see the attach.

For security reasons attached file is password protected. The password is “22663″.

The Management,
The Polynode.com team
http://www.polynode.com

[Attached file: Document.zip]

I was never aware I had such a diligent and resourceful management team working for me. Three cheers, guys, for keeping me safe from those dreadful proxy-relay trojan viruses. It’s a good thing I installed this software that you sent me, or else I’d sure be in trouble!