You wanted to know how it's calculated.
That was the supposed amount of ETH that was stolen. 1 ETH is currently around $2800. The value it has is because people are buying ETH for that price. So you take $2800 and multiply it by 400000. Carry the 5, etc. That's $1 120 000 000.
There was some other stuff stolen too I think. I haven't really looked into it.