Each time you request blockchain data from a wallet, the server may be able to view your IP address and connect this to the address data requested. Each wallet handles data requests differently. If privacy is important to you, use a wallet that downloads the whole blockchain like Bitcoin Core or Armory. Tor can be used with other wallets to shield your IP address, but this doesn’t prevent a server from tying a group of addresses to one identity. For more information, check out the Open Bitcoin Privacy Project for wallet rankings based on privacy.

From a widespread adoption standpoint: for the typical consumer, Bitcoin is technically challenging and cumbersome to use for the inexperienced. They also forfeit the consumer protections afforded by traditional credit and debt cards. Merchants already have incentive to accept it in the form of reduced fees for accepting payments over typical payment processors.

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This is particularly problematic once you remember that all Bitcoin transactions are permanent and irreversible. It's like dealing with cash: Any transaction carried out with bitcoins can only be reversed if the person who has received them refunds them. There is no third party or a payment processor, as in the case of a debit or credit card – hence, no source of protection or appeal if there is a problem.
An ASIC (application-specific integrated circuit) is a microchip designed for a special application, such as a particular kind of transmission protocol or a hand-held computer.  An ASIC is a chip designed specifically to do only one task. Unlike FPGAs, an ASIC cannot be repurposed to perform other tasks. An ASIC designed to mine Bitcoins can only mine Bitcoins and will only ever mine Bitcoins. The inflexibility of an ASIC is offset by the fact that it offers a 100x increase in hashing power compared to the CPU and GPUs, while reducing power consumption compared to all the previous technologies.
No. 5: Coinbase (online exchange). Online exchanges are, by and large, less secure than the methods described below. But Coinbase seems to have learned from the lessons of its predecessors, and is one of the biggest bitcoin exchanges in the world. It's also user friendly; not only can you buy, sell, exchange and trade bitcoin on Coinbase, but you can store your bitcoin in a wallet there, too.

Computing power is often bundled together or "pooled" to reduce variance in miner income. Individual mining rigs often have to wait for long periods to confirm a block of transactions and receive payment. In a pool, all participating miners get paid every time a participating server solves a block. This payment depends on the amount of work an individual miner contributed to help find that block.[82]

Bitcoin prices were negatively affected by several hacks or thefts from cryptocurrency exchanges, including thefts from Coincheck in January 2018, Coinrail and Bithumb in June, and Bancor in July. For the first six months of 2018, $761 million worth of cryptocurrencies was reported stolen from exchanges.[60] Bitcoin's price was affected even though other cryptocurrencies were stolen at Coinrail and Bancor, as investors worried about the security of cryptocurrency exchanges.[61][62][63]