A few days ago I did some summer cleaning on my computer, moving a bunch of old files to an external Flash drive for backup and then deleting them from the computer. To make sure that no one could recover my old photos or videos, I used this program called Eraser to wipe the free space after I moved the files. I used the Guttman method (35 passes) to wipe the free space on my hard drive.
Is there any way someone could recover this data even after I wiped it with 35 passes? Let's say I sold my hard drive on Amazon and someone bought it. Would they be able to do it?