Detecting fake and bad microSD cards, USB drives & flash memory

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This guide is not meant to scare you but to help prevent you from losing valuable data due to  fake memory.
16GB and above seems to have the most common fakes. But lower capacities should be checked if they are going to be used for important data. Popular brands are commonly counterfeited. Unusually cheap drives are to be avoided.
Check the official manufacturer's pictures and specs (Sandisk, Kingston, Samsung) to see if the capacity actually exists or if there are differences in design.
TOP: is from the official website and is the authentic product.
BOTTOM: The bottom is from a search an is not authentic. Note the design differences.

Then check the sellers neutral/negative feedback. You can also search through positives with negative messages if practical.
If you are seeing several feedback messages in the manner of:
"Had several problems with memory card."
"Data kept getting corrupted on memory card"
The seller should be avoided. Even buying flash memory at "normal" prices or from domestic sellers you may end up with a fake, especially for the high capacity flash memory.

2.  Do not use your card for important data once you receive it. You can test it with two methods.
Fill it with data that is unimportant or easily replaced.
If you encounter the following problems:
  1. Corrupted data.
  2. Frequent need to reformat.
  3. Difficulties with saving files.
  4. Extremely sluggish performance, especially with large files.
The memory is defective or fake. 
You can also test your flash memory with a program called h2testw (it will initially open in German but can be switched to English). If you are pressed for time you can try filling it to 30% capacity but testing to the full amount is highly recommend.  
If you see the message in your test results, "The media is likely to be defective." with a large amount of data lost, your card is bad. A should be reported as counterfeit if you see a company's trademark being misused or open a case for significantly not as described if you can not obtain a refund.

Even if your card is genuine, you should always keep backups of your important data as their small size makes them easy to lose or damage.

Images are covered under fair use for purpose of teaching.
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