Against the background of increased market activity, Poloniex, the largest exchange of altcoins, suffered a DDOS. Although the exchange was able to neutralize this problem, many users still report problems related to the implementation of transactions and the Bitcoins withdrawals. Users complain that a few hours later their withdrawal has not yet manifested in their wallets, and Poloniex is not officially in a hurry to admit the problem.
The DDoS began on the night of May 9, as it was then that access to the exchange limited for few hours. Poloniex posted on official Twitter account:
"DDoS; we're working to mitigate."...
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https://bit.news/eng/how-does-a-temporary-freezing-of-transactions-at-poloniex-affect-the-users/