Poloniex is the single largest holder of STEEM dollars on the network, with $1413316.560!
No one else has even close to that much.
The reason they have so much is because other steamians import their steem into the poloniex account in order to trade on the poloniex exchange.
But today Poloniex has shut down the deposit and withdrawal of all SBD due to "maintenance or...network/wallet issues."
But thats not all!
According to coingecko, the market cap of STEEM dollars is 3 million USD.
If you approximate 1USD=1SBD, that means that poloniex has sieged 1.4M out of the total supply of 3M SBD, or roughly HALF THE STEEM DOLLARS!!
Even though this bug will hopefully be patched soon it is still worrisome that half the SBD in circulation could disappear if poloniex went down for good.