Fight SPAM - Here's how

1. Retrieve the SPAM-article and look at the headers.
2. Look for the lines: PATH, NNTP-Posting-Host and Message-ID. (The Message-ID can be faked.)
3. Figure out the spammer's domain (with the help of a trace/DNS-lookup util).
4. Send a friendly mail to abuse@[spammer's domain] and postmaster@[spammer's domain] and include a copy of the headers (and part of the message-body).
Here's an example:

Subject: Usenet spam

I wish to draw your attention to the attached Usenet posting. It is a
commercial advertisement posted to a binaries newsgroup by a user from your
domain. It's totally irrelevant to the group it was posted to.
Such vandalism just makes the whole system less useful to everybody.
Please get it stopped.
Thank you!

RR.
RRFAS@hotmail.com
---------------Copy of Usenet post--------------

5. Remember that staying polite is the best weapon against spam.
6. Consider subscribing to a free mail-service (like hotmail or nightmail) in case an unfriendly domain-owner decides to send you a mail-bomb.

Or,

If you don't feel like going to so much trouble, try this:

Send a copy of the offending post to the address at the bottom. Be
sure to include all header fields. Your newsreader should have an
option that allows you to display all header fields. Cut and paste the
entire header, along with the first line or so (to save bandwidth) of
the post and email it to UNET Technologies. If these pinhead spammers
get enough complaints logged against them, then their domain will be
revoked.

UNET Technologies, Inc.
Web:    http://www.uu.net
Mail:   fraud@UU.NET            (MassMail Complaint)
        spam-complaint@UU.NET   (Usenet Complaint)