Delete your MacOS HDD

When I left Microsoft I wanted to wipe my hard drive for security reasons. But the usual format c: did not attract me because any clever guy could restore my private information.
Therefore I needed to erase my data with some kind of security tool.
Unfortunately these tools come with a price tag. I searched for free software and did not find any for Windows. I took a peek at what the Open Source world had to offer and found a quite good command called dd. Unix minimalism: Nice.
The only way to use that command on Windows is to download a free LiveCD of a Linux distribution of your choice. I tried SuSE first but it was too bloated for my likings.
I switched to something more lightweight like Knoppix.
After shutting down Windows7 and booting from the freshly burned CD I opened a terminal in Linux and typed:

dd if=/dev/urandom of=/dev/sda bs=1M

I used the dd command with the urandom parameter. This populated any disk with random data. It takes about two hours for 250GB and seems secure.