Bitcoin surpassed $19,000 today and is up about 170% year to date. The cryptocurrency is now just slightly below its all-time high of $19,783 reached in December 2017.Unprecedented monetary and fiscal stimulus has boosted the best-known digital currency as its supply is limited. Interest from billionaire investors like Paul Tudor Jones and Stanley Druckenmiller and wider mainstream acceptance of cryptocurrencies have further fueled the surge.Last month, PayPal (PYPL) announced the launch of a new service enabling its users to buy, hold and sell cryptocurrency directly from their account. Square (SQ) and PayPal clients are buying most of the new bitcoin supply, per CNBC.Investors interested in bitcoin and other cryptocurrencies should be aware of the risks before they decide to invest. These are very volatile and usually go through boom-bust cycles. Unlike real currencies, which are issued by central banks, cryptocurrencies have no central bank backing. Further, there have been many instances of hackers stealing bitcoins.The Greyscale Bitcoin Investment Trust (GBTC) acts as a bitcoin fund but is not an ETF. Several ETF providers have filed for cryptocurrency ETFs, but all those applications have been rejected by the SEC so far. Shares of GBTC, which are eligible to be held in certain IRA and other brokerage accounts, however, usually trade at a premium to their NAV.Blockchain, the technology that underpins cryptocurrencies, is still very new, and its full potential is not yet known but many experts say it could change the global economy.There are four blockchain ETFs investors could look at. The Amplify Transformational Data Sharing ETF (BLOK) and the Reality Shares Nasdaq NexGen Economy ETF (BLCN) have gained between 50% and 53% this year. Overstock (OSTK), Square, PayPal, Nvdia (NVDA) and AMD (AMD) are among the top holdings in these ETFs.Please watch the short video to learn more.Want key ETF info delivered straight to your inbox?Zacks’ free Fund Newsletter will brief you on top news and analysis, as well as top-performing ETFs, each week. Get it free >>Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report NVIDIA Corporation (NVDA): Free Stock Analysis Report Advanced Micro Devices, Inc. (AMD): Free Stock Analysis Report Overstock.com, Inc. (OSTK): Free Stock Analysis Report PayPal Holdings, Inc. (PYPL): Free Stock Analysis Report Square, Inc. (SQ): Free Stock Analysis Report Reality Shares Nasdaq NexGen Economy ETF (BLCN): ETF Research Reports Grayscale Bitcoin Trust (GBTC): ETF Research Reports Amplify Transformational Data Sharing ETF (BLOK): ETF Research Reports To read this article on Zacks.com click here. Zacks Investment Research Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report