???Very careful when buying bitcoins, ethereum etc to exchange for onions, Kraken and Poloniex Holdings based in San Francisco and Delaware respectively suffered serious denial of service (DDoS) attacks on May 7 and 8, which led to many leveraged positions were liquidated.
A large Ethereum sales order was executed a few minutes after a DDoS attack against Poloniex. This was a sufficient volume sales order to push down significantly the Ethereum price and therefore liquidate positions that were leveraged.

During the attacks, both sites were not working properly and many users could not connect to manage their account and control their positions. The exchanges, in turn, may have to settle the positions of the users based on the margin calls.
This happened in May, it's good to be smart with new happenings, back up your wallets on a flash drive.