PGP Shredding is really safe?
I would like to know if shred method with only 1 pass is really secure for data exclusion. I do this question because it is written in PGP Shred: "PGP Shred exceeds DoD 5220.22-M media sanitization requirements at 3 passes. While more passes are allowed, modern disk hardware does not require more than 2 passes."
When I erases a data, only 1 pass overwrites the cluster. Why I need more than 1 pass?
The CIA, FBI, NSA, Interpool or another institution have a software or "hardware scanner" to recover the shredd data?
I searched this in web for many months but not come to a conclusion. I wrote a message to the Western Digital asking this but the response was not conclusive. The manufacturer of HDD do not want to talk about it; in the internet foruns the users speculate about it; and I'll go crazy!
Sorry for my bad English! I'm learning yet.