Dogecoin, a cryptocurrency which started off as a joke, has jumped in value by 50% after inventor Elon Musk dubbed it "the people's crypto".
Cryptocurrencies such as Dogecoin and Bitcoin are generated by computers. Their supposed value comes from the finite number that can be computed.
Dogecoin uses a Shiba Inu dog as its mascot and is based on a meme featuring the animal.
The currency has risen more than 800% in the year so far.
After reaching a high of $0.058 (4.2 pence), each dogecoin is currently changing hands for about $0.046, suggesting a total value for all 128bn coins of about $5.89bn.
It was created in 2013 by a pair of software workers after one of them made a joke about the next big cryptocurrency, according to an interview with Vice.
However, with no intrinsic value like gold or land, and no ability to generate an income like a company or bond, cryptocurrencies are extremely volatile and can crash as fast as they rise.
This makes them hard to value and makes their prices susceptible to tips from backers or sudden panics.
Critics point out that while any given cryptocurrency may have a finite supply of units, the number of cryptocurrencies is ever-growing and potentially limitless.
People have lost large amounts of money in steep drops in the value of cryptocurrencies and in hacks and corrupted or lost hard drives.
Bitcoin's value dropped by $5,000 on 4 January to about $29,000 before recovering the lost ground. On 11 Jan, it dropped $9,000 to $32,000.
Because the cryptocurrencies can pass international borders quickly and are not regulated like cash or regular investments, investigating thefts is hard.
Last month, the Financial Conduct Authority (FCA) issued a stark warning to investors in so-called cryptoassets.
The financial watchdog said investors should be "prepared to lose all their money" should their investment's value collapse.