Some call it the most famous pizza purchase in history: In May 2010, a programmer called Laszlo asked an online forum if anyone would buy him a couple of pies in exchange for 10,000 Bitcoins, an experimental online currency launched in 2009.

“No weird fish topping or anything like that,” he wrote.

With each Bitcoin fetching less than a cent at the time, the order was worth about $41. Today, it would be valued at about $1.4 million (1.08 million euros).

As of Friday, a single Bitcoin traded at around $135, with the currency nearing $147 earlier in the week — up from about $20 at the start of February. It’s a stratospheric jump some claim has been fuelled by Cypriots and Russians seeking to invest their euros elsewhere during Cyprus’s banking crisis, stoking fears that a new online bubble might soon burst.

“It’s completely irrational,” said Yannick Naud, a portfolio manager at the London-based Glendevon King Asset Management firm, who has seen an increase in client queries about Bitcoins. “As an investor you can’t put any underlying value on the Bitcoin itself.”