It is a while since I had a go at cracking MacPrefect, Foolproof, Empower etc but they can all be beaten. As long as the disk is not encrypted.
They typically work by writing a flag in the partition table that says the hard disk is write protected. The special partition that the Mac uses to identify a bootable device (the "hard disk driver") is also rewritten, so that it preloads the protection software before the OS. As the OS loads, the protection software applies itself again, allowing the OS to modify the hard disk, but not users. The really clever protection apps also encrypt the hard disk.
As I wrote in my first reply, you can only crack it by suppressing the drive when the Mac boots. If you simply boot from another drive, allowing the internal drive to mount, the protection code is loaded when the Finder looks at the drive. However, if the disk is not mounted, you can do what you like with formatters and block editors.