Porn when printing

Well I got a highly unusual phone call from a web site customer
who said that a user called to complain that when the customer's
page was printed - porn appeared at the bottom of the page.

The porn didn't show up on the user's (or anyone else's) browser,
and our server doesn't have anything on it resembling the porn.
So I'm confident the server can't be implicated.

But I'm curious: anybody heard of something like this?
A munged print spooler at the user site, perhaps?  Or a virus?

-John

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