Your Credit Card Record Is Not So Anonymous, New Study Reveals

If you think your anonymized credit card data is protecting your privacy, think again.

According to scientists at MIT, it only takes four simple pieces of outside information—like where you shopped, what you bought, and when—to unmask your identity with 90% accuracy.

Let that sink in.

Just four facts, and your supposedly anonymous data isn’t anonymous at all.

Even worse?

If one of those facts is the price of the item, researchers only need three clues to pinpoint who you are in a dataset of over a million people.

This means your online footprint—those innocent Instagram stories, Facebook check-ins, and tweets about where you had brunch—might be all anyone needs to connect you to your entire purchase history, even without your name attached.

“We’re building this body of evidence showing how hard it actually is to anonymize large sets of data like credit cards, mobile phones, and browsing information,” says Dr. Yves-Alexandre de Montjoye, the lead researcher from MIT.

And if you’re thinking, I don’t spend that much or post that often, here’s the bad news: women and high-income individuals were even easier to identify.

This study may have just obliterated everything we thought we knew about data privacy.

How Four Clues Can Unmask Millions

To understand just how exposed your data really is, we need to look at what de Montjoye and his team actually did.

Over the span of three months, they analyzed the anonymized credit card records of 1.1 million people.

The kind of data many companies claim is “safe” to share or sell because it’s been stripped of names, account numbers, and other personal identifiers.

But the MIT researchers weren’t buying it.

They wanted to test how easy it would be to reverse-engineer those anonymous records using data from the real world. So they gathered:

Purchase details from 10,000 brick-and-mortar shops
Publicly available information from social media platforms like Instagram, Twitter, and Facebook

If someone tweeted about their latte art at 10:30 a.m., tagged their location, and then posted a shopping haul to Instagram later that day, that was more than enough for researchers to line those activities up with a single record in the anonymized data.

“Those four clues didn’t have to include anything about what had been bought,” reported Aviva Rutkin for New Scientist. “Although a guess at the approximate price of the transaction did sharpen their accuracy.”

In many cases, this allowed them to identify the individual behind a credit card record with eerie precision.

Meet “Scott” — Or, How Anyone Can Be Found

To illustrate how shockingly easy this process is, here’s a real-world example from the study.

Imagine someone went to a bakery on September 23, and a restaurant on September 24. That doesn’t seem like much to go on, right?

But in the dataset of 1.1 million people, only one person matched those two purchases on those two days.

The researchers gave him a pseudonym: Scott.

“We now know all of his other transactions,” the study reads. “Such as the fact that he went shopping for shoes and groceries on 23 September, and how much he spent.”

With just two seemingly innocent actions—grabbing a pastry and dining out—Scott’s entire purchase history was exposed, including items that might have been deeply personal or revealing.

This wasn’t a fluke. It was the norm. And it makes clear just how fragile “anonymized” data really is.

Wait—Isn’t Anonymized Data Supposed to Be Safe?

Here’s where this story really turns upside down.

We’ve been led to believe that anonymization is a bulletproof privacy measure. Strip the name, blur the ID number, maybe round off the timestamps, and voilà! The data is safe.

But this study, and previous work from de Montjoye’s team, prove that’s a dangerous myth.

Back in 2013, the same research group showed they could match people to their anonymous phone records with a 95% success rate.

All they needed was a few data points about where and when a person had made calls.

The implications of that earlier study were unsettling enough.

But this new research goes further, because your spending habits are often even more revealing than your location.

Where you eat, what you buy, when you spend—it creates a data fingerprint so distinct that even small fragments of outside knowledge can match it to your identity.

“We really need to think about what it means to make data truly anonymous,” said de Montjoye. “And whether it’s even possible.”

The Common Assumption That Just Got Shattered

Now here’s the pattern interrupt—the moment where we challenge everything you thought was true.

You’ve probably been told your personal data is safe because it’s anonymized.

That companies can use your information for research or marketing without violating your privacy.

This study shows that’s flat-out wrong.

Even when your name is removed, your life is still etched into your data.

And if anyone with access to public clues decides to dig—even casually—they can reconstruct who you are, where you go, and what you spend.

What makes this even more disturbing is that many companies resell this kind of “anonymized” data, sometimes to marketers, sometimes to insurance providers, and sometimes to data brokers you’ve never heard of.

And while the intentions may not always be malicious, the risk is massive.

Because once your metadata has been matched to your identity, everything else you’ve ever done in that dataset becomes an open book.

How Big Data Became Big Business—At Your Expense

You might wonder: Why is this kind of data even being collected in the first place?

The short answer? Money.

In the digital economy, your data is currency.

Every online purchase, Google search, YouTube view, or Amazon click becomes a puzzle piece in a billion-dollar surveillance economy.

Advertisers use it to target you more precisely.

Tech platforms use it to refine their algorithms.

And third-party brokers bundle it into massive data sets that get sold, sliced, and resold—often with the promise that it’s been “anonymized” and is therefore harmless.

But as MIT’s research makes clear, those reassurances are increasingly meaningless.

In fact, the more data that exists about you—both anonymized and public—the easier it becomes to de-anonymize anything.

You might think that sharing a quick snap of your burger on Instagram is harmless.

But pair that with a tweet about a sale you went to, and a tagged Facebook check-in—and you’ve just handed over the key to your data vault.

The Legal Loophole You Didn’t Know About

There’s another wrinkle here that makes the whole situation worse.

In most countries, privacy laws protect what’s called “personally identifiable information” (PII)—things like your name, email address, or Social Security number.

But anonymized data isn’t considered PII.

So companies can legally share or sell it without your consent, as long as they remove your name.

Even if that data can still be tied back to you with a handful of clues.

This creates a massive loophole—one that many experts say needs to be closed.

“We hope research like this will convince governments around the world to update their laws,” says Paul Schwartz, a privacy law expert from the University of California, Berkeley.

Because right now, the legal system is several steps behind the technology.

And that leaves your privacy hanging by a thread.