Ghosts of exchanges past return to haunt the bitcoin scene, as MtGox creditors line up to stake their claims at the bankruptcy court in Japan? In the US the crypto-currency broke new ground as a US presidential contender said he would accept bitcoin donations.

Elsewhere, bankers' attitudes toward bitcoin continue to oscillate between threat and promise, while regulators make ponderous progress on the road to regulation. And in Spain bitcoin is now VAT-free.

The MtGox story gets murkier by the day

Lead investigator Kim Nilsson at bitcoin security specialists WizSec released the results of his recent work delving into the transaction records of failed bitcoin exchange MtGox, which collapsed in early 2014 owing around $500 million (£329 million) of client funds.

According to Nilsson, 'most or all' of the lost bitcoins were in fact stolen over a period 'beginning in late 2011'. The coins were taken directly from MtGox's 'hot wallet' - the reserve of bitcoins kept online by the exchange to maintain enough liquidity to conduct business.

It is best practice for exchanges to keep most of their clients' bitcoin deposits offline in cold storage. It's not clear that MtGox was doing this, because if it had been, the funds in its custody could not have been stolen in this way.

'MtGox operated at fractional reserve for years (knowingly or not), and was practically depleted of bitcoins by 2013.

'A significant number of stolen bitcoins were deposited onto various exchanges, including MtGox itself, and probably sold for cash (which at the bitcoin prices of the day would have been substantially less than the hundreds of millions of dollars they were worth at the time of MtGox's collapse),' Nilsson reports.

You can read his full report here.

That's not the end of the story, though. Rumours that the collapse of MtGox was an inside job persist. One school of thought has it that the stratospheric rise in the price of bitcoin in November 2013 - it rose from $200 to its all-time high of $1,236 on 4 December - may be related to individuals unknown at MtGox 'gaming' the market.

The price run-up coincided with a peak in the activity of two automated dealing computer programs, or bots, dubbed Willy and Markus. It is alleged by some in the industry that the bots were controlled by someone familiar with the inner workings of the MtGox exchange.

The bots repeatedly placed buy-only orders, thereby pushing the price higher and inflating volumes on MtGox, which was by this time well on its way to becoming the largest bitcoin exchange in the world.

But the story doesn't end there. Enter the FBI, allegedly.

As readers of this column will know, the Silk Road dark web marketplace was shuttered following an FBI sting operation in October 2013, leading to the prosecution and an eventual guilty verdict being handed down to Ross Ulbricht, aka 'Dread Pirate Roberts', the operator of the site.

Now two FBI special agents involved in that investigation, Carl Force and Shaun Bridges, have been arrested and accused of stealing thousands of dollars worth of bitcoins.

Force is alleged to have extorted money from Ulbricht. This was all going on while Force was an executive at the digital currency exchange CoinMKT. Bridges allegedly stole $820,000 and deposited it at MtGox.

According to prosecutors, two days later his signature was on the warrant that led to the seizure of millions of dollars worth of bitcoin from client accounts at the same exchange. Of course all these interconnections may just be a series of coincidences, but there are those who smell a rat.

Beyond the world of subterfuge and crime, on 22 April MtGox customers were at last given permission by legal authorities in Japan to lodge claims against the exchange. The bankruptcy trustee has set up a page on the MtGox site for claims to be registered.

Regulators making moves

European Union financial markets regulator, the European Securities and Markets Authority (ESMA), has opened a consultation into how digital currencies and their associated public online ledger blockchain technology could be used in investments.

The ESMA reveals that it has been monitoring the bitcoin industry for the past six months and has now decided to 'call for information' from ecosystem participants.

It follows a similar consultation by HM Treasury started last year and the conclusions from which were released in a report that coincided with the Budget in March.

Meanwhile, in New York the much-discussed 'Bitlicense' (sic) could soon see the light of day. Matt Anderson, deputy superintendent for public affairs at the New York State Department of Financial Services, told Coindesk earlier this month that it was still sifting through the submissions to its consultation process.

'We take some time to review the comments for potential changes or modifications, and hopefully [will] publish a final rule soon,' says Anderson, adding that the BitLicense that will be at the centre of the state's regulatory framework for digital currencies will be out 'very soon'.

UBS sets up innovation lab in London

London's position as a hub for financial technology development was further cemented this month when investment bank UBS announced the opening of a research lab focused on digital currencies.

Group chief information officer Oliver Bussmann says in a statement that the lab will be based at fintech incubator Level39 in London's Canary Wharf district.

'We are moving away from a purely in-house innovation strategy, optimising collaboration opportunities with the growing FinTech business, start-up and investor community in an open and transparent way,' he explains.

BBA sees potential threat from bitcoin

A British Bankers Association paper entitled 'The Digital Disruption: UK Banking Report', published in late March this year, highlights the threat to banks posed by digital currencies and the importance of the trade association's member banks taking immediate action to mitigate the risks of disruption to their businesses.

The report notes the hurdles that bitcoin and other digital currencies still face before they can gain wide acceptance, but nevertheless suggests the currency could become 'part of the broader ecosystems that customers are constructing around themselves'.

The report's authors relate a conversation with a British banker who likened today's banking industry to a castle protected by a moat (regulation) and the digital innovators as attackers armed with a new weapon - canons - that render the moat useless.

Although the report sees no such killer app on the horizon, 'as [digital currencies] grow in popularity, so too will the risks for banks'.

Viva España

In a boost to bitcoin usage by consumers, Spain's General Directory of Taxes has said that goods and services paid for with the digital currency will not be subject to VAT, the sales tax of the European Union.

German and UK tax authorities have taken a similar approach in the absence of a ruling from the European Union, while Poland and Estonia do not exempt bitcoin transactions from VAT.

Rand Paul - the libertarian bitcoin pioneer

US politician Rand Paul, senator for Kentucky, recently announced that he is running for president. The republican contender is on the libertarian right of the party and has a reputation for railing against what he sees as the inflationary largesse of the US Federal Reserve, the US's central bank.

He has long been a supporter of digital currencies as a tool for undermining the Fed and so, true to his principles, has said he will accept campaign contributions in the form of bitcoin as well as US dollars.

LeoCoin hit by 'pyramid scheme' allegations

UK-based company, Learning Enterprise Organisation (LEO), this month announced the opening of a trading platform for its LeoCoin digital currency, which it touts as an alternative to bitcoin, claiming it to be the second-largest crypto-currency in the world.

The coin's founders, Dan Anderson and Atif Kamran, say the coin already has 30,000 merchants signed up and 100,000 entrepreneurs.

However, the pair have since attracted criticism for their involvement in UNAICO Pakistan, whose activities the Pakistan securities authorities say 'broadly fell' within the definition of 'fraudulent activities', after receiving complaints that it was operating a pyramid scheme.

LeoCoin's business model includes an element where current users recruit others in a similar way to pyramid scheme members.

Anderson and Karman both deny the claims. LEO said in a statement to financial news broadcaster CNBC that the allegations against it were 'completely untrue'.