FROM_MAILER problem

I recently had a spam sneak through filters with the following
header:

        From: mailer_daemon151(_at_)yahoo(_dot_)com

First appearances are that this was identified by the FROM_MAILER
"macro" in procmail v3.11pre7  Is this possible?  I had thought
that this macro _wouldn't_ match on mailer addresses that included
numbers in the userid?  Or do I need to add a test for "fudged"
mailer addresses?

Confused,

Dave Stone