Just took a look for this and think I've found the exploit that people are using.
As PenguinAvenger said it is a glitch/exploit that exists on both the PS3 and XBox 360. It also exists on the Wii U due to it being ported, just like the majority of glitches and exploits that we end up with.
An equally nasty and game breaking exploit still exists on BO2 but has yet to be patched because support was dropped before I could get the info to A_Trey_U. I'm still sitting on the details and proof of it being used. To make the matter worse there are more people using this same exploit due to it not being patched.
I know that the game has been hacked on the other platforms and people will be quick to either claim to use hacks in order to appear "cool" or want to blame it on hacks, but the Wii U, PS4 and XBox One are currently hack free. This is just a glitch/exploit that is being abused.