When Wikipedia went dark and Google blacked out its logo on Wednesday, millions of people could not help but notice. For most, it was the first time that they had heard about two antipiracy bills. One puzzled Twitter user wrote: “Isn’t a SOPA some kind of food?”

But that protest grew out of a much wider grass-roots movement — a collective flexing of Internet muscle that started in some of the less mainstream parts of the Web, like the social news site Reddit and the blogging service Tumblr, and in e-mail chains and countless message boards.

It is no coincidence that these social sites were among those that, according to critics of the legislation in question, the Stop Online Piracy Act, and the Protect Intellectual Property Act had the most to lose if it passed. And by design they were able to take the message about the threat and make it go viral.

In the resulting groundswell, lawmaker after lawmaker renounced support for the legislation. Fight for the Future, a nonprofit organization that helped organize the protests, said more than 115,000 Web sites participated, and three million people e-mailed Congress to voice their opposition to the bills. “The tech community is using its own technology to rally around the issue,” said Ron Conway, a Silicon Valley patriarch who has invested in hundreds of start-ups, and runs SV Angel, an investment fund. “We probably wouldn’t prevail here if we weren’t eating our own dog food.”