A photographer buys a 128GB microSD card for a wedding shoot. The card fills up across the day, the camera shows no error, and the files copy to a laptop that night. A week later, half the photos are corrupted, and the ones past the 32GB mark are gone entirely. The card was never 128GB. It was a 32GB card with a reprogrammed controller that reported a bigger number, and everything written past the real capacity overwrote itself into nothing.
That is the counterfeit SD card scam, and it is one of the oldest in electronics. The counterfeiter takes a small, cheap card and reprograms its controller to report a much larger size. The operating system believes the number. The camera believes the number. Nothing checks the number until the data is already lost, because the card accepts every write and quietly discards or overwrites whatever does not fit.
An SD card has two parts that matter: the flash memory, which stores the data, and the controller, which tells the device how much memory there is. The counterfeiter reprograms the controller to report a size the flash cannot hold. A 32GB card reports 128GB. A 64GB card reports 512GB. The printing, the hologram, and the packaging prove nothing, because all of it is copied from the real product, and the card itself looks identical to a genuine one.
The giveaway is the price and the capacity. A 2TB microSD card does not exist as a real product, so any listing that sells one is selling a fake. A 1TB card at a third of the retail price is the same story. The other giveaway is the seller: a marketplace account with a handful of reviews, a name that looks generated, and a price that undercuts every authorized retailer. Genuine cards from authorized sellers cost what they cost, and the discount is the tell.
There is exactly one way to know a card's real capacity: write data to every part of it and read it back. The standard tool on Windows is H2testw, version 1.4, which writes test data across the whole card and verifies it. On Mac and Linux, the equivalent is f3write and f3read, and f3probe is a faster variant that tests the card without writing to all of it. A card that reports 128GB and fails at 32GB is a fake, and the test result is the proof.
The test takes time, because it writes the full capacity, but it is the only test that matters. A speed test does not prove capacity. A visual inspection does not prove capacity. Checking the serial number does not prove capacity, because counterfeiters clone real serial numbers too. The write-verify test is the one check that cannot be faked, because it measures the flash itself rather than the controller's claim about it.
For a marketplace, the SD card scam is a pattern problem, not a single-listing problem. The same seller account lists the same fake capacities across multiple card types, the prices cluster below the authorized range, and the reviews arrive in bursts after the listing goes live. A monitoring system that watches seller behavior, price anchors, and review timing catches the pattern before a buyer does, because the fake card's listing looks like the last fake card's listing.
For a buyer, the defense is simpler: buy from an authorized seller, run the write-verify test on arrival, and return the card the moment it fails. A card that passes the test is genuine enough to use. A card that fails it was never the capacity on the label, and the data you were going to put on it is worth more than the refund.
If this topic is useful, these earlier guides go deeper on connected questions: Fake phone chargers: the listing tells, and the safety tests that expose them, Counterfeit earbuds: the listing tells you before the sound does, and Counterfeit smartwatches: what monitoring catches that a glance misses.
Run a write-verify test: H2testw on Windows, or f3write and f3read on Mac and Linux. The test writes data across the whole card and reads it back, and a card that reports 128GB but fails at 32GB is a fake. Packaging, holograms, and serial numbers prove nothing, because counterfeiters copy all of them.
It is lost or overwritten, and it is unrecoverable. The card accepts the write because the controller says there is room, but the flash memory has nowhere to put it, so the data overwrites earlier files or vanishes. That is why the corruption shows up weeks later, when you try to read the files back.
No. There is no real 2TB microSD card on the market, so any listing that sells one is selling a fake. The same applies to any capacity far above what the major brands sell at that price. A card that undercuts every authorized retailer by half is not a bargain, it is a reprogrammed smaller card.
Usually not the device itself, but it can corrupt the data on it, and a card that fails mid-write can freeze a camera or corrupt a file system. The bigger risk is data loss: photos, video, and documents written past the real capacity are gone. Test every new card before you trust it with anything important.