When wiping data with some programs you get different levels of 'security', i.e. the number of times they overwrite the data.
A basic level may be just overwriting it with 0's or random binary numbers, with a more secure solution being to do this 3 times (the standard) or an even more secure solution being to overwrite it up to 35 times.
Why would you have to do it more than just once? Surely when the code is changed it can never be taken back, so what's the need for overwriting it repeatedly?