The Gutmann data sanitization method is often implemented in the following way:
- Pass 1 - 35: Writes a random character
In reality, the Gutmann method uses a complex pattern of overwriting from Pass 5 through Pass 31. There is a lengthy explanation of the original Gutmann method here including a table of the patterns used in each pass.
Erasing a hard drive using the Gutmann data sanitization method will prevent all software based file recovery methods from finding information on the drive and is also likely to prevent most hardware based recovery methods from extracting information.
Note: The Gutmann method was originally designed for a different kind of hard drive than used today and, because of this, is probably overkill. Peter Gutmann himself said here in an epilogue to his original paper that "For any modern ... drive, a few passes of random scrubbing is the best you can do."
Most data destruction programs support multiple data sanitization methods in addition to the Gutmann method.