They come in many forms and it is very difficult to tell a real one from a fake, for almost any memory card you can buy there are fakes. We have seen fakes of all sizes and none of them have anything like the capacity that they are advertised as. Some sellers that sell them put disclaimers in their descriptions that the memory sticks may not be of the expected capacity and will be in a range of x - y GB and it is the buyers responsibility to make sure the capacity is correct. There is one VERY big problem with this. When the memory stick is opened on the computer it shows the size that was expected for example 32 GB or 64 GB or whatever the size was advertised as. This leads into the main problem. Whilst the physical capacity of the memory stick may only be 4 or 8 GB the device will let you continue to add data to the device long after that limit is reached. It does this by allocating an area of the memory stick where folders, filenames, etc are stored (or the ROOT Directory) and this generally remains OK as do the first few GB of data written. Once the physical capacity is reached, the device then goes back and starts to OVERWRITE data.
That's right, it OVERWRITES data replacing it with the new file. What happens now is that for as long as you copy files, they will continue to copy until the fake size limit is reached, then and only then will it tell you the device is full. The user will only become aware that anything is wrong when they try to read one of the overwritten files and find it is corrupt.
Can we recover?
Generally no, all we can get are a few files near the beginning and sometimes a few from the second part of the device. You would be able to get these yourself with free data recovery software.
How can you tell the difference between genuine and fake memory cards?
This is very difficult, firstly though if the device comes with packaging read it carefully, look for obvious spelling and grammar mistakes that you would not expect to see on a top-name branded memory stick. If it does not come with packaging, then look at the quality of the device, does it 'feel right'
We are currently in the process of writing free software to determine if memory sticks are capable of holding the amount of data they claim to hold. There are also other tools available free online.
The software is now available for download. You will need to follow these instructions carefully.
At the end of the test you will be notified that either the card is most likely genuine or a possible fake. If it is a fake it will show the size that is available for data entry.
There is a help file in the program that can be accessed through the menu or by pressing the F1 key that give full instructions and some examples of tests we performed whilst writing the software.