A hacker on Friday siphoned more than $50 million of digital money away from anexperimental virtual currency project that had been billed as the most successful crowdfunding venture ever — taking with him not just a third of the venture's money but also the hopes and dreams of thousands of participants who wanted to prove the safety and security of digital currency.

The attack most likely puts an end to the project, known as the Decentralized Autonomous Organization, which had raised $160 million in the form of Ether, an alternative to the digital currency Bitcoin. While the computer scientists involved in the project are aiming to tweak the code that underpins Ether in a way that will recover the money, the theft is nevertheless prompting a bigger debate about the viability and principles of virtual currencies like Bitcoin and Ether.

"This is one of the nightmare scenarios everyone was worried about: Someone exploited a weakness in the code of the D.A.O. to empty out a large sum," Emin Gün Sirer, a computer science professor at Cornell who co-wrote a paper pointing out problems with the project, said on Friday.

Central banks and financial firms have been exploring how to use the technology underlying virtual currencies — known as blockchain — to improve their own internal systems. The technology is considered to have advantages in terms of transparency and security. Just last week, Janet L. Yellen, the Federal Reserve chairwoman, told central bankers at a trade industry conference that they should accelerate their efforts to explore blockchain.

But the incident on Friday provided another reminder of how the code can be just as vulnerable to human greed and mistakes as paper bills.