Bulgarian police have seized enough Bitcoins to pay off a fifth of the country's national debt after the value surged by 600% in half a year.

Officers are said to have confiscated hundreds of thousands of units of the virtual currency worth $500million from an organised crime gang in May, reported Daily Mail.

But the surging value of Bitcoin means that the haul of 213,519 is now worth a staggering $3.3billion.

That is enough to pay off almost a quarter of Bulgaria's national debt, although it is not known what the authorities have done with the currency.

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Dozens of offenders were arrested in May following an investigation by the Southeast European Law Enforcement Center into an alleged customs fraud.

The organisation, which comprises 12 member states, said at the time: "The offenders choose the Bitcoin way of investing/saving the money, because it is rather difficult to be tracked and followed."

The virtual currency is made up of lines of computer code which are digitally signed each time they travel from one owner to the next.

Transactions can be made anonymously, making the currency popular with libertarians as well as tech enthusiasts, speculators - and criminals.

Originally the currency was worth just $1 per unit - although this has surged to an all-time high of more than $16,600 amid violent market swings this month.

Tech-savvy users called "miners" use their computers to make complex calculations in a bid to verify that a 'block' of Bitcoin transactions are genuine.

It is similar to cracking a code - and it takes more than 1.7billion attempts each time using an enormous amount of computing power as well as electricity.

Users often combine their processors virtually to work together completing millions of calculations per minute between them.

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In reward for their efforts, the miners who crack each code are rewarded with a share of the currency in the form of 12.5 newly created Bitcoins.

But for the average person, the costs involved with mining are so high that it is no longer worth getting involved.