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]

Because it's similar to gold mining in that the bitcoins exist in the protocol's design (just as the gold exists underground), but they haven't been brought out into the light yet (just as the gold hasn't yet been dug up). The bitcoin protocol stipulates that 21 million bitcoins will exist at some point. What "miners" do is bring them out into the light, a few at a time.
Once again, Bitcoin is dangerously close to the local lows. Since June, we have many times seen that bulls stand up for protection of the benchmark of the cryptocurrency on the falls to around $6100. Meanwhile, reversals to decline on the BTCUSD pair are happening on low levels. Last week, the reach of just $6500 became a turning point to the next reversal. It ...
Although Bitcoin is innovative and massively influential, it has some problems that developers are trying to fix with their own products. There is an altcoin that makes faster transactions, there is an altcoin that is less volatile, there is an altcoin that is more private and so on. There are more than one and a half thousand altcoins on the market at the day this text is written, according to Altcoins are playing a very important role by expanding boundaries of blockchain possibilities and the scope of applications.

As more miners join, the rate of block creation will go up. As the rate of block generation goes up, the difficulty rises to compensate which will push the rate of block creation back down. Any blocks released by malicious miners that do not meet the required difficulty target will simply be rejected by everyone on the network and thus will be worthless.
Bitcoin faced extreme headwinds in March when Alphabet's Google (ticker: GOOG, GOOGL) joined Facebook (FB) in banning ads for cryptocurrencies, which lowered liquidity in the market. In an abrupt reversal, Facebook said on June 26 that it would allow some ads for cryptocurrencies, but continues its ban against initial coin offerings and binary options.
Bitcoins are mined with powerful computer hardware and software. A maximum of 21 million Bitcoin will be available, after which no further bitcoins will be produced. The algorithm which governs the production of Bitcoin limits the quantity that will be produced, and the rate at which they will be produced. It is a finite commodity – there is a fixed amount, and that ensures that greater demand will always prop up the price. In this way, it is similar to other finite commodities such as crude oil, silver, or gold.