On Halo Reach, there are classified weapon kills on career stats. There is a blank one which many people say they haven't obtained yet. Somehow, I have managed to get 27 of these kills on New Alexandria. The only out-of-place thing i remember doing is the phantom/pelican driving glitch then killing enemies with the phantoms boost. Here is a link on how to get the vehicle.
http://gamerglitch.com/glitches/halo-reach-glitches/new-alexandria-glitches-fly-pelican-or-phantom/
Can anyone confirm this or shed some light on my thoughts.