Activity around bitcoin has reached fever pitch recently. REUTERS Bitcoin gained another 6% Wednesday, reaching a new high for the year.

The cryptocurrency reached the $450 mark late in the day before falling back to $425. That's compared with around $250 a month ago.

What's behind this? Investors and brokers can't agree.

In the last few days, explanations have included a rise in demand from China, an upcoming auction by US Marshals of seized bitcoin, and the influence of a convicted Ponzi schemer's latest gambit.

Another catalyst for recent appreciation comes from Europe, says Adam White, vice president and product manager at Coinbase, one of the biggest bitcoin exchanges globally by volume.

The European Court of Justice recently ruled that the cryptocurrency is exempt from the region's "value added tax," which White compared to the decision by US taxation authorities in the 1990s to not implement taxes on goods sold online.

What is certain is that use of bitcoin by consumers and trading is broadly on the rise.

"There has been a steady increase in the number of transactions processed on the bitcoin blockchain," White says.

In the last two years, the number of bitcoin transactions has increased threefold from 50,000 daily to about 140,000 today, according to Blockchain.info, which tracks bitcoin data.

It is true that Chinese investors are eager to trade bitcoin, White says.

In the US, between 300,000 and 500,000 bitcoin are traded daily, White said. But in China, that daily figure has been closer to 1 million to 1.2 million.

That isn't to say US investors are neglecting the currency. There has been a three-times increase in the relative trading volume by what are referred to as "High Net Worth" traders on Coinbase's trading platform — people making trades in dollar amounts worth up to six figures, White said.

Perhaps most telling — at least about the recent jump — is that there's been a recent surge in trading, sharp rise in new user sign-ups, according to White.

So what's behind the recent surge in bitcoin? Maybe just the surge in bitcoin.