Obviously the most vital part of your entire OVERDRILL run, triggering the secret.
When the drill is done, head on into the vault hallway. But keep in mind, do not destroy any of the four cameras in the hallway!
Alright, we're in the vault hallway, we've taken out the guards. Now what? Now we trigger the secret. If you still are fighting an assault wave, and you're on hard or above, I suggest you wait out the assault wave before attempting to trigger the secret.
When you're set to take your spots and trigger the secret, here's what to do.
This is a static that was revealed as the community was still working on cracking the secret. If you have a look, there's 8 squares, 4 arrows and some text saying "MURUA X". The text is mostly irrelevant, what you want to pay attention to is the squares and the arrows. The squares represent the pillars in the vault haullway, the arrows represent the players. I like using X as the desk in the hallway. What you want to do now is to line up like the arrows, one crew member stands behind the desk, another one is by the entrance looking at the man over at the desk. One crew member stands between the last two pillars in the hallway to the right of the member behind the desk, looking over to the elevator shaft on the opposite side. By the elevator shaft is the final member, who is to look down the hallway at a wall.
The secret won't always trigger right away, which is explained here
, so fidget around your spot a bit, stand still and fidget about some more until you hear a C4 beep. The right side of the desk in the hallway will now flash red.
At this point, I'd recommend pouring out the thermite, but don't jump into the vault when it's done. You'll do that as you complete the rest of the heist.