1) Privacy is paramount. We have no need to see or pass on the personal information stored on the hard drive(s) of donated computers. And people who donate computers to C4C should do so without fear that any of their personal information will be compromised.
2) Staying within the law. A commercial operating system (like Windows or Mac OS X) left on the hard disk has a license that won't be passed on to the new owner. The same holds true for any commercial software, music, videos, etc.
How exactly are the hard disk drives wiped?
C4C uses DBAN, dd, or wipe to wipe the hard disk drive(s) of donated computers Whatever the method; all previous information is obliterated; pictures, music, videos, documents - even the operating system.