An example of a nothing at stake attack is an attacker buying lots of "old stake" from users inexpensively (inexpensive to users who no longer have stake in the currency). This can be made convenient by offering small payments to users for uploading their wallet.dat. Eventually after accumulating enough "old stake", the user can begin creating blocks and destroying as many or more coin days than the network was at that time. This block generation can be repeated until it catches up to and beats the current main-chain very cheaply.
The screenshot below, taken from the site, might help you put all this information together at a glance. You are looking at a summary of everything that happened when block #490163 was mined. The nonce that generated the "winning" hash was 731511405. The target hash is shown on top. The term "Relayed by: Antpool" refers to the fact that this particular block was completed by AntPool, one of the more successful mining pools. As you see here, their contribution to the Bitcoin community is that they confirmed 1768 transactions for this block. If you really want to see all 1768 of those transactions for this block, go to this page and scroll down to the heading "Transactions."
Blockchains are secure by design and are an example of a distributed computing system with high Byzantine fault tolerance. Decentralized consensus has therefore been achieved with a blockchain.[29] Blockchains solve the double-spending problem without the need of a trusted authority or central server, assuming no 51% attack (that has worked against several cryptocurrencies).
A large portion of this risk is credited to Bitcoins’ unconventional price fluctuations. Unlike the fiat markets, where fluctuations are limited to a few pennies, Bitcoin sees differences in whole dollar amounts. It can be perfectly illustrated in Bitcoin’s fall from some $1,000 to the current $225. Investors however believe that that the digital currency was in a speculative state where it suffered a lot of manipulations from bad actors. With growing adoption, this manipulative tactics are being reduced and Bitcoin is attaining a stable value. With stable, they mean a $10-20 fluctuation on a bad day.
Bitcoincharts is the most popular website for following the current bitcoin price. The site provides a rundown of all major btc exchanges by volume. You can also arrange the markets to only display the Euro or the Japanese Yen versus bitcoin on the different exchanges. Like the name says, the website also offers charts with several popular technical indicators. The choice of timeframes ranges from 1 minute all the way to the Weekly TF. Plus, you get to see the current market depth at the different exchanges.
Bitcoin is not perfect! The system is powerfully designed, but it is the first widely-used cryptocurrency. As such, as it grows to a large scale crypto-commodity, we are beginning to notice problems and challenges that would have been next-to-impossible to predict when bitcoin was first designed and implemented. Many altcoins have been developed specifically to address concerns raised over the future and long-term viability of bitcoin.
Altcoins can differ from Bitcoin in a range of ways. Some have a different economic model or a different coin-distribution method, like altcoins that were given away to all citizens of a country. Others employ different proof-of-work mining algorithms, perhaps to resist specialized mining hardware — or maybe they don’t even rely on proof of work at all. Several altcoins offer a more versatile programming language to build applications on top of, while yet others offer more privacy compared to Bitcoin. And there are also altcoins that serve very specific, non-monetary use cases, like domain name registry or data storage pointers.

This is the most popular Bitcoin pair in the world. Bitcoin uses peer-to-peer technology to operate with no central authority or banks; managing transactions and the issuing of Bitcoins is carried out collectively by the network. Bitcoin is open-source; its design is public, nobody owns or controls this cryptocurrency and everyone can take part. Bitcoin price grew significantly within a short period of time making the BTC/USD pair quite popular among active traders and investors. Through many of its unique properties, Bitcoin allows exciting uses that could not be covered by any previous payment system.
ETC could be poised to survive for one major reason: Ethereum is moving towards a proof of stake system. Some people will undoubtedly want to use ETC over the new protocol because they prefer proof of work consensus. Coinbase also recently added ETC, which is a good sign this coin isn;t going anywhere soon. For these reasons, Ethereum Classic is a good investment.
no pb for payment, the service is fine. However, it lacks a confirmation that "you have begun to mine", because except the one of the payment, nothing indicates that it works ... we remain in the expectation ... (as far as the 1st mining does not appear until 24 hours later and that the 1st payment will not intervene before 16j for the BTC) it lacks a little message...
Altcoins began life as little more than bitcoin copies attempting to mimic bitcoin’s successful run, but they quickly became much more than their name suggests. At the time of writing (February 2018), there are more than 1,500 altcoins available for use. While many are still struggling to break the mold set by bitcoin, some are doing truly amazing things with the technology.
Cryptocurrencies are a potential tool to evade economic sanctions for example against Russia, Iran, or Venezuela. In April 2018, Russian and Iranian economic representatives met to discuss how to bypass the global SWIFT system through decentralized blockchain technology.[56] Russia also secretly supported Venezuela with the creation of the petro (El Petro), a national cryptocurrency initiated by the Maduro government to obtain valuable oil revenues by circumventing US sanctions.

EOS has other technological strong points as well. For instance, it is fast and more scalable than Ethereum. Where the Ethereum Network requires users to pay gas to use the network, EOS does not have gas fees as transactions are approved by a centralized group of 21 gatekeepers. EOS also has huge and enthusiastic community support, and for good reason. The coin is not mined. Rather, block producers are voted in by the community. Finally, EOS recently completed a successful token sale and has the capital to develop its full potential. For these reasons, I am confident EOS will be a profitable investment in 2019 and beyond.
But where are the bitcoins actually stored? After you install one of the two clients above, you can find your bitcoins in a file called wallet.dat. If you use windows this file will be located in the application data section. If your computer gets stolen or lost and you haven’t made a copy of the wallet.dat file you will lose your bitcoins. It is always recommend to backup this file.