Paypal, the eBay-owned mobile payment system and the world's second biggest, announced that it would soon let customers pay in bitcoin, the virtual currency. The catch, for the moment, is that merchants will have to agree to accept the use of bitcoin, which for some could be problematic.

Still, the announcement is a major commercial milestone for bitcoin, which has had its ups and downs as backers have fought for acceptance. "Fairly or not," wrote Wired, "bitcoin still has an image problem. For every VC who extols the innovative power of the digital currency, pop culture still sees it as a way for the paranoid cyber-libertarian to shop for black-tar heroin on the Silk Road. All the more reason, then, that bitcoin fans should rejoice" at the Paypal deal.

In a move announced Monday at Techcrunch's Disrupt conference, PayPal is supporting the cryptocurrency on its Braintree payments platform. When the Internet's most mainstream brand for moving money embraces a technology, it's hard to see that system as a fringe operation.