You probably know the blockchain best as the technology that underpins Bitcoin and other digital currencies. As a kind of automated ledger, it's ideal for tracking the movement of currencies. Because it's decentralized, those transaction records can't be changed. And because it can't be changed, the rewards given to users who give up resources to power the ledger can't be altered either. The blockchain is clear. It's transparent. And its ability to maintain a currency has already been proven.

But the blockchain can do so much more. It's a complete market disruptor that's already changing the sharing economy and the financial sector.

And now it's disrupting marketing.

Online advertising faces a challenge. About one user in twenty in the United States now uses ad blockers to stop websites showing them commercials as they browse the Web. Users are concerned about privacy and they're increasingly cautious about working with online advertising companies that are collecting huge amounts of their data. They don't want to see the ads and they don't want some giant company to see what they're doing. Facebook and Google are starting to wake up to the problem but a real solution lies not inside companies but in decentralized systems like blockchains.

That's because current marketing depends on knowing what a user has done in the past. Facebook, Google and other companies track what we do on the Web and try to predict what we want to do in the future based on the data they've collected about us.

Decentralized, blockchain marketing is based on what someone is doing at that particular moment. Instead of giving rewards in the form of discounts, offers, and content to people in return for their data, a blockchain is in the perfect position to reward participation now.

It already does this. Bitcoin miners receive Bitcoins when they write blocks of transactions into the blockchain. Other blockchains, though, could give tokens to people for sharing content or for completing a level in a game or for making a post. Those tokens can help to motivate real purchases.

And again, it's already happening.

Never Stop Marketing has compiled a long list of companies now active in blockchain-based marketing ventures. They include Minds, a Pinterest-like social media platform that pays cryptocurrency for contributing to the community, and Karma which works in a similar way on an Instagram-like platform. BravoCoin, is like a blockchain-powered Yelp or TripAdvisor, while Presearch is a search engine that offers to pay people who search.

What each of these companies does--and there are many more working in the same space--is reward users for using their product, instead of for giving up their data. They can also keep track of content, a benefit for content creators who are worried about the Internet's habit of stealing and sharing intellectual property.

This is all very new. None of these companies is yet a household name, though the same was true once of Google and Amazon. But the technology that underpins this new form of marketing is already proving its worth and could soon change the way brands promote themselves.