When you delete sensitive files from a disk on your computer, the operating system usually does not erase contents of these files from the disk - it only deletes references to these files from filesystem data. The deleted file's body remains unchanged on the disk and can be easily recovered using special disk utilities.
Wiping is a term used to describe a process of shredding contents of a file or disk space. It is impossible to restore any data that has been properly wiped.
The BCWipe software is intended to give you a confidence that your deleted files cannot be recovered by an intruder. BCWipe repeatedly overwrites special patterns to the files to be destroyed. BCWipe for UNIX offers two wiping schemas: