In May 2018, Bitcoin Gold (and two other cryptocurrencies) were hit by a successful 51% hashing attack by an unknown actor, in which exchanges lost estimated $18m.[72] In June 2018, Korean exchange Coinrail was hacked, losing US$37 million worth of altcoin. Fear surrounding the hack was blamed for a $42 billion cryptocurrency market selloff.[73] On 9 July 2018 the exchange Bancor had $23.5 million in cryptocurrency stolen.[74]

There are also "stake grinding" attacks which require a trivial amount of currency. In a stake[2] grinding attack, the attacker has a small amount of stake and goes through the history of the blockchain and finds places where their stake wins a block. In order to consecutively win, they modify the next block header until some stake they own wins once again. This attack requires a bit of computation, but definately isn't impractical.
Zcash, like Monero, offers greater privacy to users. Unlike Monero, transactions are shielded rather than made completely private. Meaning, the details of the transaction itself, such as the users involved and the amount traded, are hidden. Zcash does this by using a “zero-knowledge” proof that allows for parties to exchange funds without revealing each other’s identity.
Around 2008, Satoshi Nakamoto founded Bitcoin. At the time, a paper was published through the Cryptography Mailing List. The first Bitcoin software client was released in 2009, and he collaborated with many other developers on the open-source team, careful never to reveal his identity. By 2011, the enigmatic Bitcoin founder had disappeared. His peers understood how valuable this cryptocurrency was, and worked feverishly to develop it to its maximum potential.