Investing.com - A new website has been created, outlining the estimated hourly cost of carrying out a so-called 51% attack on various cryptocurrencies, highlighting the risk to smaller coins.According to 51Crypto, Bitcoin would cost $564,909 per hour to attack, making it the most expensive target, because of the large size of its blockchain.A 51% attack happens when hackers gain control of more than half of the mining power on a cryptocurrency network, allowing them to tamper with the blockchain ledger where transactions are recorded.A single digital coin can even be spent more than once, in what’s called a double spend.The website notes that Bitcoin cannot actually be attacked with this much money as the total renting capacity of the hashing power required is well below what would be needed, while one hour would not be enough time to make such an attack profitable.Smaller coins with widespread listing on exchanges would be much cheaper and easier to attack