Secure deletion algorithms There are several algorithms of secure deletion:  

Single Pass – data area is overwritten once with “1” or “0”.

DoD Method – the data area is overwritten with 0’s, then 1’s and then once with pseudorandom data.

Guttman Method – the data area is overwritten 35 times. This method overwrites the drive taking into account the different encoding algorithms used by various hard drive manufacturers.

NSA erasure algorithm – data is overwritten seven times with “0” pattern then with “1” and so on. It is the best method for quick and secure deletion (QuickWiper can do it).