It has been pointed out that there is a risk of critical information leakage from recycled/discarded PCs. But, the number of information leakage cases is not decreasing.
If you put a file in Recycle Bin and delete a file from Recycle Bin in Windows, a file seems to be deleted. Despite you intended to delete files, lots of files can be restored by a commercial file-restoring software. Even if you format a hard disk or re-install OS from a recovery CD-ROM, a risk of information leakage never changes.
"Disk Shredder 4" erases hard disks' data completely, by overwriting meaningless data such as random numbers on every sector of hard disks.
It is recommended to erase data completely by yourself, when you recycle/discard PCs or when you return PCs to rental/leasing companies.
Why don't you use "Disk Shredder 4" to protect information leak with easy operation?
FAQ on the necessity of Disk Shredder 4