If you’ve ever set up Customer Match, enhanced conversions or a conversions API, you’ll have heard the reassurance: don’t worry, the data is hashed. It sounds like encryption. It sounds like nobody can read it. It’s worth understanding what actually happens.
What hashing does
Hashing turns a piece of text into a fixed string of characters. Put in an email address and a function like SHA-256 gives you a long jumble of letters and numbers. The same input always produces the same output, and you can’t easily run the process backwards.
Why that doesn’t protect anyone here
The platform receiving your list already knows millions of email addresses: the ones its own users signed up with. It hashes those in exactly the same way, then compares the two lists. Wherever your hashed customer matches its hashed user, it knows precisely who that person is. That’s the whole point of the feature. It’s called matching for a reason.
Hashing hides the address on the way there. It doesn’t hide the person from whoever receives it.
So hashing protects the data while it travels. It doesn’t stop the receiver from recognising the person at the other end. For your customer, the result is the same as if you’d sent their address in plain text: they’re now identifiable to an advertising system, because they bought something from you.
It’s also weaker than it sounds on its own terms. Email addresses and phone numbers follow predictable patterns, so a hashed list can be reversed by simply trying every likely address. The US Federal Trade Commission said as much in 2024: hashing doesn’t make data anonymous.
Doesn’t customer consent fix it?
Not for us. A cookie banner that says “Accept” may make tracking legal. It doesn’t make it what the customer came for. The Nullware Standard isn’t a legal minimum: members don’t ask customers to agree to be handed over, and a click on a banner doesn’t change the rule.
What this means for members
The Standard treats hashed identifiers exactly like unhashed ones. Emails, phone numbers, names and customer IDs don’t go to marketing platforms in any form: hashed, encrypted, uploaded by hand or sent quietly from a server.
What to do instead
You can still find out what’s working. None of these need anyone to be followed:
- Campaign links and promo codes. Tag the links in each campaign and give each channel its own code. Your own analytics and your till do the rest.
- Aggregate conversion counts. Count sales per campaign inside your own tools, without tying them to a person.
- Ads without feedback. Buy ads with the platform’s own targeting, and judge them on your own sales. Just don’t send anything back.
- Just ask. A one-question “how did you hear about us?” at checkout is still one of the most reliable signals there is.
Most of these tell you more about why people buy than a matched audience ever did. And none of them turn your customers into someone else’s inventory.