Haram means illegal, I don't see any special and logical reason behind the bitcoin is illegal. Day by day it's gaining popularity among the people who engage in virtual work. So i 100% believe that its is totally contradict the people idea about haram of bitcoin because its 100% halal (legal).
There is no consensus yet, for each party's theory and argument.
1. The first party "Not allowed": Its like "Haram," but it means that there are reasons for prevention such as High volatility, no profit guarantee. [Islamic Sharia sanctifies money and thus prevents anything that leads to wasting money or gambling]
2. The second party "unknown": This is the rule of the Bitcoin when most Muslim scholars.
Since There is no consensus among all Muslim scholars."Religious fatwa" It is up to the laws of states/countries.
Dollar, Pound, Euro and all others currencies are Haram?
Islam only recognizes the origins/currencies associated with gold or silver.