Bitfinex

Prices of cryptocurrencies NEO, OMG and ETP crashed close to 90 percent on the Bitfinex exchange before reverting back to normal levels; the crash caused the closure of many accounts that made leveraged trades and lost those accounts thousands in potential profits; Bitfinex claims the exchange worked as it should in the situation, but traders disagreed and complained via social media about the crash as well as demanding refunds; the site was slow to respond and traders unable to access their accounts according to complaints; incidents like this test the overall cryptocurrency markets as many believe they are unstable and not safe. Source.