I cherish these people. From the wipe manpage:
I hereby speculate that harddisks can use the spare remapping area to secretly make copies of your data. Rising totalitarianism makes this almost a certitude. It is quite straightforward to implement some simple filtering schemes that would copy potentially interesting data. Better, a harddisk can probably detect that a given file is being wiped, and silently make a copy of it, while wiping the original as instructed.
Recovering such data is probably easily done with secret IDE/SCSI commands.
My guess is that there are agreements between harddisk manufacturers and government agencies. Well-funded mafia hackers should then be able to find those secret commands too.
Don't trust your harddisk. Encrypt all your data.