We've observed some adult spam in disguise. The usual adult spam that we see is simple text with links and adult phrases that make it quite obvious what it is. The mutation that we've recently observed includes an email that has two parts -- HTML and plain text -- where the plain text portion looks completely legitimate and in fact is a portion of a legitimate newsletter of some kind. However, the headers make it apparent that it is not from the legitimate company.

more at securityfocus.com