Questions about the security of Bitcoin (BTC) emerged on May 18, when the F2Pool mining pool released six consecutive blocks in the BTC block chain, which included block numbers 630804 to 630809. Many exchanges and other Bitcoin-related services only question whether Bitcoin is still secure enough because it only requires three confirmations before removing funds. Is mining mixed power centralized? As we reported earlier, the hash rate on the network has dropped by 30% since last week’s Bitcoin half event. This is largely due to reduced miners’ rewards, mining has become unprofitable on older machines, and margins are already tight. However, the distribution between competing pools in this mixed network continues in a generally balanced way. Although F2Pool is clearly the largest mining pool, it accounts for less than 20% of the overall hashrate. To rate an attack on the network, this rate should be 51%. Technically, although F2Pool can add transactions in its favor to one of the previous blocks and somehow take advantage of it, there is no way to predict it will extract six blocks in a row. Everything can only be described as an example of probability. If you throw a coin six times, it is unlikely that you will take the tour six times. But if you throw a coin repeatedly at long intervals, you are more likely to witness a series of six rounds. Since you do not know when this will happen, your profit from such a bet is also very low. Similarly, there is no way for F2Pool to profit from this coincidence, because it is almost impossible for them to know that this will happen.