Bitcoin is, by a considerable margin, the most popular cryptocurrency today. In the original paper written by the elusive Satoshi Nakamoto one of the fundamental principles was what was termed "proof of work". However, the concepts behind the way in which that proof of work is supposed to operate may just have been undermined in a paper published by researchers from the University of Illinois.
In Bitcoin the proof of work is the same as was defined in a previous generation of virtual currency called hashcash. In order to generate Bitcoins you have to solve the mathematical problem set out in the definition of the proof of work - a process that theoretically everyone trying to solve the problem is equally likely to solve. It is exactly this process that Bitcoin Miners undertake to earn their reward of Bitcoins.
The problem for Bitcoin Miners, and some would say Bitcoin as a currency, is that the original definition of Bitcoin means that the reward for solving the problem progressively decreases over time so that eventually the true economic costs of mining Bitcoins means that it will no longer we worth doing so for the reward it attracts. This means that there is a likely to be a limit to the number of Bitcoins ever generated (estimated to be around 21 million).
