shred is a command on Unix-like operating systems that can be used to securely delete files and devices so that it is extremely difficult to recover them, even with specialized hardware and technology; assuming recovery is possible at all, which is not always the case.

To prevent this, shred overwrites the contents of a file multiple times, using patterns chosen to maximize destruction of the residual data.

However, since wear leveled devices do not guarantee a fixed relationship between logical blocks addressable through the interface and the physical locations in which the data is stored, shredding may not provide adequate security.

[2] The scrub command overwrite sequence of data being compliant with a Dec. 2005 draft of National Nuclear Security Administration Policy Letter NAP-14.x.

Written by Jim Garlick of LLNL, it offers a selection of overwrite sequences, though all ultimately suffer from the same limitations outlined above.