A decentralized digital currency that enables low-cost payments without the need for central authorities and issuers. Bitcoin is a peer-to-peer (P2P) currency system created in open source C++ programming code. Bitcoins can be accessed from anywhere in the world with an internet connection. Once a user has Bitcoins, they are stored in a digital wallet. Bitcoins can then be sent to anyone else who has a Bitcoin address. Bitcoin was developed in 2009 and based on the works of an individual or group of individuals known as Satoshi Nakamoto
Can the stock market rally go on?
The new year has begun with stock markets in the UK and US hitting new record highs.
The Dow Jones Industrial Average rose above 25,000 points for the first time this week, while the broader S&P 500 is also at historic highs.
In London the FTSE 100 closed on Friday at a new record high of 7,724 points.
But could stock markets on both sides of the Atlantic change tack and come crashing back to earth this year?
Business calls for more Brexit clarity
Vicky Pryce, chief economic advisor at CEBR, says the uncertainty about the shape of Britain's departure from the European Union has meant many companies - both domestic and foreign - have been unwilling to make long-term commitments.
Ideally they want as little change as possible from the status quo, she adds, and believes that the government is "slowly moving in that direction".
For Roger Bootle, chairman of Capital Economics and a high-profile Brexit supporter, he hopes the UK is able to strike a "deep and special" trade relationship with the EU.
But he is not too worried if that is not the outcome: "I think it's perfectly possible for Brexit to deliver some very good results for the UK even if we don't get that deal."
Exmo Bitcoin exchange manager freed by kidnappers
Kidnapped Exmo Bitcoin exchange manager Pavel Lerner was freed by his abductors in Ukraine on Friday.
Exmo confirmed that their employee is safe and "there was no physical harm inflicted on him".
Mr Lerner, 40, a leading analyst at the cryptocurrency company, was kidnapped on 26 December while leaving his office in Kiev's Obolon district.
According to Ukrainian media reports, Mr Lerner was "thrown out on a motorway" by his abductors.
Exmo said: "Pavel is currently in a state of major stress, therefore, he will not provide any official comments in the coming days.
"The case is currently under investigation of the state security authorities."
The company emphasised it was back to business as usual, and that Mr Lerner did not have access to any financial assets on the platform.
'Unknown masked people'
Mr Lerner is a prominent Russian blockchain expert and the news of his kidnapping has stunned many in the international cryptocurrency community.
Blockchain is the technology that underpins the digital currency Bitcoin.
Exmo confirmed that Mr Lerner was kidnapped by "a group of unknown masked people".
Russian and Ukrainian media reports said he was dragged into a black Mercedes-Benz by men wearing balaclavas.
Police in Kiev confirmed to the BBC that a man had been kidnapped on the day and location in question, but would not confirm his identity.
A spokeswoman said that the matter was currently under investigation, and that more information would be made public later on.
Exmo Finance is registered with Companies House in the UK, but has its main operations in Ukraine.
According to its website, it has 94,955 active users trading cryptocurrencies.
Separately, Exmo said in a tweet that it been the target of a cyber attack on Thursday.