While Bitcoin was initially described as an anonymous currency, its transactions are recorded on a public ledger that can be tracked and traced by law enforcement. Each Bitcoin user has an address, made up of letters and numbers, and the authorities are often able to link an address to a real person using sophisticated data analysis. In contrast, Zcash uses a method developed by a team of cryptographers working at M.I.T. and in Israel — known as zk-Snark — that allows transactions to be confirmed by the network without anyone recording the Zcash addresses involved in the transactions. Users can opt out of this privacy function.

http://www.nytimes.com/2016/11/01/business/dealbook/zcash-a-harder-to-trace-virtual-currency-generates-price-frenzy.html?_r=0