“This is the first blink of awakening of the world to a danger that’s been present for a long time, which is that we are exposed,” Mr. Searls said. “Cambridge Analytica is old, old news to privacy folks.”

John Scott-Railton, who researches digital rights and privacy at the Citizen Lab at the University of Toronto, said he recently thought back to all the PowerPoint presentations and papers he had given and seen that cautioned about how third parties might access and abuse user data.

“It didn’t stick until now,” he said. “Now it’s changed, or at least people nod along when we talk about it.”

Neema Singh Guliani, legislative counsel at the American Civil Liberties Union, recalled the organization’s years of efforts to get Facebook to monitor how third parties were using data. Yet few paid attention at the time, even though the group specifically called out Facebook’s quizzes in 2009. (Cambridge Analytica used a third-party quiz app from an independent researcher to harvest Facebook users’ data.)

The social network has said it will investigate many third-party apps that have had access to large amounts of users information. Nonetheless, the A.C.L.U. is pushing for users to have tighter control over what Facebook apps can do and arguing that Facebook ought to audit its developers. The organization also believes that more privacy protections should be enshrined in law.

“We’re having the conversation now that we should have had over a decade ago,” Ms. Singh Guliani said.

Some privacy experts are prepared for disappointment. There have been privacy scandals before that did not lead to sea changes. For example, Google once collected private Wi-Fi information as it was building out Google Maps. The ensuing outrage did not have a lasting effect on the Silicon Valley company’s vast data collection effort.