&gt; The upside of this is that none of them have been able to break the basic blockchain mechanism and profit from doing so. That&#x27;s an impressive achievement in computer security.<p>Not really. Merkle trees aren&#x27;t exactly new, and neither is the transaction signing mechanism used in Bitcoin. Bitcoin didn&#x27;t achieve anything novel here.<p>The major new idea Bitcoin brought to the table was proof of work. However, Satoshi couldn&#x27;t predict mining pools, which has led to the situation Bitcoin is essentially controlled by a small cabal of miners and core devs. This is not the decentralized system Satoshi envisioned.<p>In fact, there have been cases in the past where a single pool actually had &gt;50% of mining power for short periods of time. Since ownership of pools is not exactly transparent, we have no way of knowing if any pool out there is currently at 50%, or if there are multiple pools colluding. The classic argument is that there is no incentive for a 50%+ miner to hurt the network, but then you&#x27;re trusting a random pool owner with your money, which goes against everything that Bitcoin set out to do.<p>Moreover, a large pool has been known to game satoshi dice by including a double-spend in its next block if it lost, and thus denying the original transaction to go through. Other games like selfish mining can be played as well.<p>Your statement that Bitcoin remains unbroken is not really true. A double spend has been demonstrated during the first big fork (around version 0.8, if memory serves me). It was announced with proof on Bitcointalk. I guess hat since the guy was a white-hat, and returned the money, you&#x27;re still technically correct in that he did not profit from it.<p>Bitcoin is also notoriously vulnerable to DDOS attacks. We had several big DDOS events this year with Bitcoin transactions being backed up for hours, even days. In one case a company was &#x27;stress testing&#x27; the system by filling up the blocks with dust transactions, and in another an attacker found a way to very cheaply fill up blocks with certain types of transactions (sigops).<p>Finally, Bitcoin simply does not scale very well because it&#x27;s a massively replicated system that records and distributes transactions to every node in the network. This does not scale in number of nodes (network diameter, end-to-end latency) or in number of transactions (bandwidth, blockchain size).<p>All in all, calling Bitcoin an impressive achievement in computer security is a bit of a stretch imho.