There are many fake Flash Drives / Pen Drives in the market nowadays. These drives are equipped with special boards known as "Upgrade Boards" by these business people. The software in the boards is written in such way that it makes your computer detect it as a Flash Drives with the space that they wanted it to be, which they are actually not. Moreover, these Flash Drives are usually those unsold 64mb or 128mb drives from the past, remodeled, resold as new Flash Drives. Some are even given out FREE by companies with their logos embossed on them.
The most ridiculous ones that I've ever seen are 500gbs Flash Drives in the Chinese Computer Stores. The amazing thing is that most who purchase them in bulk and containers are people from the West.
Well, if you ever get one of these Flash Drives and saved your precious data in them. Consider them Gone.
Note : Buy your Flash Drives from reputable sources or those you're comfortable with.