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What factors affect the value of a Bitcoin?
It's been hovering at about $5/BTC for a few months now, slowly eeking upwards. What would cause a significant spike or drop?
Hacking and theft will, presumably, come down as more players get stable. As exchanges rise, liquidity should grow.
Major hacks or attacks on key exchanges or Bitcoin services can cause Bitcoin's price to fall quite dramatically.
Increase in popularity will slowly make the price rise. Another speculation bubble can cause the price to go up quickly.
Major investments made to Bitcoin can greatly increase the price.
All of those quick changes don't appear too likely at the moment. However, it is possible that the decrease in block reward that should happen roughly around the end of the year can double the price of Bitcoin, or make a lot of smaller miners drop out of the system.
