Kristoffer Koch was doing research on encryption in 2009 when on a whim he decided to invest a small sum in the recently-created bitcoins.
Mr Koch, now 29 and working as an engineer, only remembered the investment in April this year when he read an article about the soaring value of bitcoins.
His 5,000 bitcoins were suddenly worth around £430,000.
After spending a full day trying to remember his password, Mr Koch cashed in £116,000 by selling a fifth of his newly-acquired fortune.
After deducting 28% in taxes, the money was enough for the deposit and restoration of a flat in central Oslo, one of the world's most expensive cities.
"Not in my wildest dreams could I have imagined that they would have soared like this," Mr Koch said.
"It's bizarre. These psychological reflexes that make us attach a value to something that doesn't have any in itself."
Bitcoins can be exchanged for real money or used to purchase goods and services online.
The virtual currency is increasingly used for internet transactions and its value is extremely volatile, subject to speculation.
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