He's not wiping the whole disk, he's just cleaning up the empty space so they cannot do an undelete on his files. For that simple purpose, the script works well.

I might shrink my pagefile as small as possible so to squeeze out any paged data. Delete the hibernation file as well. Run his program and maybe defrag the disk in between runs so that nothing is left in the empty sectors. Lots of wasted space like that on modern 10-80gb drives. All this stuff is amateur forensics. Anyone that's ever used the grep or strings command knows you can find tasty little nuggets without much work.

That's why openbsd has encrypted swap. Insane, but relevant in this discussion :-)