A new craze for virtual kittens is slowing down trade in one of the largest crypto-currencies.
CryptoKitties lets players buy and breed "crypto-pets" on Ethereum's underlying blockchain network.
The game's developers told the Bloomberg news agency that CryptoKitties was a "key step" to making blockchains more accessible.
But its popularity has underscored one of the technology's biggest downsides: its lack of scalability.
Etherscan has reported a sixfold increase in pending transactions on Ethereum since the game's release, by the Axiom Zen innovation studio, on 28 November.
"CryptoKitties has become so popular that it's taking up a significant amount of available space for transactions on the Ethereum platform," said Garrick Hileman, from the Cambridge Centre for Alternative Finance.
"Some people are concerned that a frivolous game is now going to be crowding out more serious, significant-seeming business uses."
Players have spent the equivalent of $6.7 million and counting buying CryptoKitties, which can sell for as much as $114,481.59, according to third-party research from developer Niel de la Rouviere.
- The ethereum-based kitten trading and breeding game clogged the digital currency's network this week, delaying at least one token sale and forcing CryptoKitties to raise its fees.
- "From a high level, abstract point of view, this stuff is almost digital artwork, if you will. It doesn't have any inherent value other than what you think it's worth," said Joey Krug, co-chief investment officer at Pantera Capital, one of the earliest investors in bitcoin.