The site isn't loading for us here at R.net headquarters at the moment, but it's been mentioned both at HBO and now at TeamXbox that the Halo manual includes a reference to the following URL: http://www.seventhcolumn.org.

We haven't seen it yet, but apparently that URL was displaying a numeral 7 and Don't make us kick your ass in Latin (NON FACETE NOBIS CALCITRARE VESTRVM PERINÆVM).

Aside from the obvious 7 reference, it's unclear yet what, if any, the significance of seventhcolumn.org is; the name itself is registered to Yeoren (Max Hoberman), Bungie's webmaster.