This has been a season of cautionary tales about the abuse of technology.

Just in the last few months, Russian hackers figured out how to get ATMs to cough up stolen millions; North Korea malwared its way into Hollywood; and Syrian terrorists produced a series of horrifying murder videos that went viral.

The world can seem frightfully interconnected these days, but there are good stories about technology, too. I’ve written before about the way gigantic problems can be “crowd-sourced,” like when a jetliner goes missing, and the task of searching thousands of square miles of open ocean is spread across millions of personal computers.

Here’s one about children and hands.

Four years ago, a South African carpenter named Richard Van As was watching Youtube videos of oversized mechanical hands, the home-made kind you might see on a giant puppet in a parade. Mechanical hands had a special fascination for Mr. Van As, who’d recently lost some fingers in a table saw accident.

One video in particular impressed him. It had been posted by a costume prop-maker in Bellingham, Washington named Ivan Owen. Mr. Owen’s giant mechanical hand was a nightmarish-looking claw that looked like something from a horror movie, but it worked just like a human hand, with wires acting as the tendons and hinged metal fingers that curled very naturally.

Mr. Van As emailed Mr. Owen to ask if he’d ever thought of making artificial fingers for a real hand.

Mr. Owen hadn’t, but the problem intrigued him, so the two men started collaborating over the Internet and eventually developed a prototype.

Mr. Van As was pleased with the device and created a Facebook page to share it with his circle of friends.

It wasn’t long before a woman got in touch with him through Facebook to ask if he’d consider making one of his mechanical hands for her son, who was born without fingers.

Which begs the question: why would a mother ask a perfect stranger on Facebook to make a prosthetic for her child? Isn’t that what doctors are for?

It may surprise you to learn how expensive traditional prosthetics can be. And I’m not even talking here about the latest and greatest versions with tiny battery-powered servos and realistic silicon skin, which can run upwards of forty thousand dollars, and are therefore limited to first-world patients who have really good health insurance.

Setting those aside, a high quality mechanical prosthetic can still cost a cool eight thousand dollars, which puts them far out of reach of most of the world’s population.

The problem of prosthetics for small children is particularly acute, because children grow so quickly. You can’t just buy a prosthetic for your three-year-old and expect it to last until she’s sixteen.

Mr. Van As and Mr. Owen collaborated again and created a small version of their mechanical metal hand for the child. The hand was successful. Then they had a brainstorm: what if we modified our hand so that the parts could be made out of plastic with a 3-D printer?

There isn’t a 3-D printer in every household — at least, not yet — but the price of the printers has fallen below $1000, which means that there are already tinkerers and “makers” in many communities who have the capability to print durable plastic parts from plans they download from the Internet.

By this time, Mr. Van As and Mr. Owen had invested thousands of hours in their invention. They had a working prototype. They had discovered an untapped market for a low-cost, easily scalable, and broadly distributed medical device. This was a recipe for a huge business, or at least a big payday.

But instead of cashing in on their invention, they gave it to the world. They made the plans for these colorful plastic hands — which children love, by the way, since they look like a superhero’s gauntlet — freely available on the Web. They created an app which makes it simple for parents to size a hand for a growing child and customize it to her stump.

And then they created a foundation, called e-NABLE, to promote and distribute new prosthetic solutions for missing fingers, hands, and even arms.

The average cost of one of these hands — just the raw materials, since there are no patents or royalties involved — is about $50. But thanks to an ever-expanding network of volunteers to print and assemble the devices, most children get them for free.

This beautiful technology was born of Youtube; powered by email; publicized by Facebook; developed on the Web; simplified by an app; downloaded to 3-D printers; assembled with the help of online tutorials; and ultimately crowd-funded via Paypal.

Score one for the good guys.