"There is of course this possibility that future computers such as quantum computers are able to crack these kind of cryptographic hashes. That would obviously completely compromise Bitcoin."
Though the strength of the algorithm makes this unlikely, that doesn't make it impossible. "If it does occur it would have catastrophic effects," he warns us.
And while governments guarantee bank accounts against fraud and theft, Bitcoin doesn't enjoy the same safety measures. If it's gone, it's gone - with also almost zero chance of being able to reclaim the money if you do find yourself "virtually pickpocketed".
Just ask the victim of the first large-scale Bitcoin theft, who had half a million US dollars worth of Bitcoins stolen in 2011. The heist took place overnight, with him waking to an empty virtual wallet in the morning. It was, essentially, a bedroom bank raid.
But if someone wanted to cause more widespread damage, they would probably have to take control of 51 per cent of the global Bitcoin network of this virtual economy.
So while transactions themselves might be safe for now, Bitcoin users will need a more secure piggy bank if virtual currency can be truly practical and secure.
What's the future for Bitcoin?
So how far can Bitcoin actually go as a viable alternative to normal currency? "The number of Bitcoins is limited," says Lehdonvirta. "And the huge deflation that creates simply makes it unfeasible for Bitcoin to be adopted on a massive scale."
But, as he then reminds us, this might be missing the point. Bitcoin is not the only crypto-currency that exists right now, and it won't be the last.
"Now that this kind of ingenious design based on distributed cryptographic currency has been demonstrated as a working principle, people are confident to create others that address some of the shortcomings of Bitcoin," he says.
"I wouldn't be surprised in the future if we saw other crypto-currencies that will become even bigger than Bitcoin."
Really, the future of virtual currency hangs in the balance of the world economy. "Politicians need to quickly restore confidence in the Euro," says Lehdonvira. "Otherwise you'll quickly find yourself in a situation where people are moving more and more of their money into places where others can't get hold of it".