I was doing some research on Halopedia and Halo.wikia, and came across how enemies were tagged by VISR and its variants. (UNSC only- not Covenant)
Essentially, all infantry units were, by some means, tagged with a IFF tracker. When they were within a friendly's range, they were marked with a yellow dot on the motion tracker.
All other units though, that did not have a transponder registered to a UNSC frequency and were subsequently marked as enemy.
I remember reading that the IFF tracker was inserted in the back of the neck (I assume around the barcode area you see in the Landfall mini-movie), however I also read that it is set in the equipment.
Which brings me to this question: How does the HUD/VISR differentiate between flood?
Granted lore wise, we know they are enemies. I mean go figure. But as the flood combat forms still use the equipment, and don't tear out the tracker, how does the HUD/VISR differentiate between friend and foe?
I am looking for a more story based than gameplay mechanic based answer, but all replies are welcome. Thank you!