Inadvertently granting access to personal data is the single biggest concern for one-fifth of US adults who use the Internet, according to a new Forrester survey of nearly 7,000 North American consumers. And this is just one data point illustrating consumers’ increased frustration with the general deterioration of their privacy. Nearly 25% of US consumers already use an ad blocker, and 14% use some kind of cookie tracking/blocking service like Ghostery or Collusion.

No matter how hard firms resist, consumers will succeed in forcing massive changes to data collection practices, writes Forrester privacy analyst Fatemeh Khatibloo in new research. But this is actually a market opportunity for firms to leapfrog their competition’s privacy practices and build trust with their customers. Those who don’t act soon by adopting contextual privacy practices will risk massive disruption from mediator brands and aggregators (think Amazon’s Alexa and Google Now) that will act as gatekeepers for consumers’ personal data.

The result: Brands will struggle to collect first-party data and will be forced to rely on second- and third-party data for crucial marketing investment decisions — sending them back to the Stone Age of marketing.

Learn more about the research here.