The hardest kind of spams to catch are those I've called "spam of the future"--
a little plain text plus a url:

    Hey there. Check out the following: 
    http://www.blackboxhosting.com/foo

The future has arrived. I regularly see spams like this now. I still catch
nearly all of them-- headers alone would be enough to catch most current spam--
but the .3% of spam that I miss is mostly spam of the future.

In spam of the future, the sales pitch is pushed one step back. Instead of
being contained in the email itself, as in an ordinary spam, it is waiting a
click away on a web site.

This trend is encouraging, because it implies that filters are winning. Spam is
literally retreating. (This is more than a symbolic victory; each extra step
cuts response rates.)

	-- Paul Graham, in "So Far, So Good"
	    <http://www.paulgraham.com/sofar.html>