OK, let me start by saying that I think the general idea of a cryptographic currency is a brilliant one. I can definitely see Bitcoin establishing itself as a major world currency, and basically doing to fiat currencies what email did to the postal system.
However, whenever I mention Bitcoin to anyone, I strongly encourage them not to invest more than they are prepared to lose. I myself only own 10 BTC. Why? Because Bitcoin has flaws, and it has potential enemies, and I think there's a very good chance that the currency could be basically destroyed overnight.
The code. Bitcoin is not a magic black box. It's a complicated piece of open-source software, written by a community of volunteers and hobbyists with various degrees of ability. IT CONTAINS BUGS. What these bugs are and how serious their symptoms will be remains to be seen, but we have already had a few serious problems (such as the 0.7/0.8 fork) and it's likely there will be more to come.
The value of exploits. With the soaring value of Bitcoins, it is likely that it will increasingly become a target for attack. If someone can find and exploit a flaw, they can make a fortune. Due to the nature of Bitcoin, it would be almost impossible to discover the culprit or recover any losses. This was already happening when there was almost nothing to gain from it!
Government intervention. Currency manipulation is one of the core economic controls of government. Mass adoption of Bitcoin would render this tool ineffective, or even unusable. It's certainly conceivable that the US or EU could implement a blanket ban on Bitcoin trades, which would utterly cripple the currency's expansion. As we're now hitting the point where large-scale funds are buying into Bitcoin, such a move would cause a rapid exodus of significant funds, by a few small high-worth individuals over a very short timescale. This, combined with the effect of legislation, would almost inevitably trigger a large-scale panic sell-off, and there would be no market remaining to allow for the currency's revival.
Corporate sabotage. Moneygram, Western Union, Paypal. Just three examples of multi-billion dollar multinationals with business models which would be rendered obsolete should Bitcoin achieve widespread adoption. Bitcoin, despite its rapid expansion and long-term potential, is tiny compared to many large organisations which have a vested interest in seeing the currency fail. At its current size, the Bitcoin economy could be toppled for a handful of million dollars- enough to buy and sell large volumes specifically to cause huge price swings, to undermine confidence with smear campaigns, or to directly attack flaws in the software or the network that underpins it.
Fundamental flaws. The design of Bitcoin is not perfect. We're already seeing the blockchain becoming bloated by the micro-transactions of SatoshiDice. What if the volume of these were to rise a thousandfold, through deliberate flooding or simply through the natural expansion of the currency? We're already worried about mining guilds which have control of too much computing power. 51% is quoted as the minimum level required in order to subvert the Bitcoin transaction system successfully. This is not strictly true- 51% is simply the point at which an attack becomes more likely to succeed than to fail. It's perfectly possible that an entity with a significant non-majority of mining power could succeed in poisoning the blockchain with dishonest blocks. This can be attempted over and over again by a motivated group or individual, and it only needs to succeed once to cause irreparable damage to Bitcoin's credibility.
With the current public interest in the currency, the media spotlight focused on it, and the fledgling involvement of high-value investors likely to abandon Bitcoin forcefully if they foresee any potential losses, I believe that Bitcoin is extremely vulnerable at present. Any one of the problems listed could trigger a panic which would crash the currency overnight, and in a way that it wouldn't likely recover from.
So, whilst I'm not concerned about the effects of speculative bubbles, and I do believe Bitcoin is destined for long-term success, I urge caution. Please, don't invest more than you can afford to lose.
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