You think you know about Silicon Valley, but you have no idea. Even the Girls Scouts here are different. When the time of year comes around for Girl Scout cookies, there's no walking door-to-door, lugging boxes of Thin Mints. Here, thanks to Facebook events, an iPhone and Twitter-founder Jack Dorsey's payment service Square, tech-advanced 9-year-olds can sell 400 boxes in less than an hour. Because when you're a Girl Scout in Silicon Valley, that's how you roll.

Facebook's global policy manager Jud Hoffman told a few people at work that his daughter Greta and a couple of her friends would be selling the cookies. So many people wanted to buy them that he decided to set up a Facebook event. That way, his colleagues wouldn't miss the girls when they stopped by the famed Palo Alto office of the biggest social network in the world.

But what really turned the event into a tech happening was when a few hours before the girls arrived, several people said they didn't have cash or checks. Mr. Hoffman, who'd heard about Square, decided right then and there to sign up for the service. Of course, few places beyond Silicon Valley are there Girl Scout dads who know about Square as well someone at the office who just happens to have the necessary hardware on hand -- a dongle manufactured by Square to be plugged into his iPhone audio jack. By the time the girls set up their wares, the father-daughter sales team was ready to accept credit and debit cards.

"It was fantastic and ridiculously easy," Mr. Hoffman said, adding that Square was a big sales motivator. "It turned out to be an attraction for people to use their credit card just to see how cool this thing was."

Square co-founder James McKelvey lost a $3,000 blown-glass sale because he couldn't accept a credit card in his art studio. So that got him and Mr. Dorsey thinking until they came up with the Square idea. Square is a service built for iPhones, iPads and Android-powered smartphones. Users open an account, download an app and get a 2.5-cm-square dongle in the mail two days later. It's pretty much that simple.

"I think it's really cool that they just came up with that," said Girl Scout Greta Hoffman, adding that her customers were almost more into the payment service than the cookies. "They were thinking it was really cool, they kept saying, 'OMG, we can use credit cards to buy Girl Scout cookies! This is really cool!'"

And, of course, the cherry on top of this Silicon Valley concoction? A tweet from Randi Zuckerberg, of course. "Some very smart, enterprising Girl Scouts are at Facebook HQ w/boxes of cookies & @square devices. Making SERIOUS bank."