On December 4, one of the largest exchanges the Bitfinex was under the DDoS-attack again. This was reported in a its official Twitter account. Also there it is indicated that they are working on the problem to restore users access to the site.
Originally it was published a message that the site is under very high load. After about half an hour they reported that the attack was over, and the stock exchange came back to normal.
It is noteworthy that earlier, on November 26, Bitfinex had already undergone such type of attack. Other exchanges are also regularly subjected to DDoS-attacks.