I use Stacker for disk compression on my PC, and this problem of un-erased data is potentially worse with that software. Probably Microsoft's DoubleSpace suffers from the same problem. If you erase a file on a compressed partition using some of these suggestions, such as writing a pattern followed by its complement, you won't erase the whole file. That is because a repeated pattern is far more compressible than the original file contents, in most cases. A 4K byte text file may compress down to 2K on the disk, but 4K worth of repetitions of 0xff will compress down to just a few bytes! The majority of your file will not be touched at all. Norton has a "wipefile" program which overwrites files according to a government standard, but I believe it just writes constant values repeatedly. This will overwrite only the start of the file, many times. Bruce Schneier recommends including one or more passes of writing pseudorandom data to the file. Since this data is not compressible it should overwrite the whole file. The data doesn't have to be cryptographically random, just something that won't be compressed by straightforward algorithms. Hal