Counterfeits are very common on eBay now, especially the 4GB Sandisk Mini Cruzers, being offered at less than half list price ($200). Here some signs of a fake:

1. The Cruzerlock (encryption) software will not work because the fake lacks a license key.

2. The picture on the front of the package (man at desk) has a fuzzy edge to the image.

3. The black label on the Cruzer does not have the pattern of ovals on the black background; the lettering is on a solid black background. I have another "genuine" Sandisk Mini Cruzer so I could put them side by side to compare.

4. When copying large files, you may end up with folders or files with names that are strings of zeros, and scrambled content in the files. That happened to me when I tested a fake by copying a folder with about 2gb of photos. You may also get error messages if you try to reformat the flash drive.

5. Fake Sandisk will NOT be recognized by Windows ME (ie, no drive lettter appears in My Computer), as will a genuine Sandisk USB drive.

If the Sandisk goes "bad" soon after you buy it  (eg, becomes unreadable and/or unformattable, and is not recognized by Disk Management in WinXP), that does not necessarily mean you have a fake. Sandisk has major quality control problems, mainly because most of these thumb drives are made in China. Their warranty service is horrible.  I have had a request for an RMA in for 3 days with no response. They must know that people use these things for work.

Another problem with these Sandisk flash drives is that they are unbelievably slow, and do not come anywhere close to the transfer rates claimed by Sandisk.  I thought there was something wrong with my 4GB Mini Cruzer until I did some web searching and found out that they are all like that. Some more searching revealed to me that Kingston's Data Traveller Elite is a lot faster, albeit a bit more expensive. I will never buy another Sandisk product.

Postscript: I bought a Kingston 4gb Data Traveller Elite (from the manufacturer!!!).  It was expensive ($240) but has very fast transfer rates in both directions.