SEC is going to now regulate Bitcoin exchanges. Read this article: https://www.investopedia.com/news/bitcoin-price-tumbles-cryptocurrency-bloodbath-continues/?utm_source=market-sum&utm_campaign=dynamicyield&utm_term=12472725&utm_content=03/07/2018&utm_medium=email
And my post here: https://steemit.com/bitcoin/@woody26/steem-plummets-as-bitcoin-falls-due-to-sec-regulations