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IRS won a judgement to have Coinbase send them client information, trading transactions totaling more than $20,000 from 20130- 2015. This is the precedent for IRS to come after all cryptocurrency trading activity on all platforms.
Keep good records of your trades in cryptocurrencies and follow the law. The law is coming.
https://techcrunch.com/2017/11/29/coinbase-internal-revenue-service-taxation/