It's also explained in the shred manual itself, that seems like a decently authoritative source to me: https://www.gnu.org/software/coreutils/manual/html_node/s

It's also explained in the shred manual itself, that seems like a decently authoritative source to me: https://www.gnu.org/software/coreutils/manual/html_node/shred-invocation.html https://www.gnu.org/software/coreutils/manual/html_node/shre... — halfway the page all the caveats are listed up to & including forensic analysis of magnetic traces of the deleted data.