well First you can read here the meaning of CEH:
http://en.wikipedia.org/wiki/Certified_Ethical_Hacker
well I will try to explain:
CEH training fortifies the abilities to guard against the weaknesses and vulnerabilities of network infrastructure and illegal hacking.
So the man behind that scaning,testing and hacking the system because he want to secure the system better.
So although he is using hacking and scans on the system he is NOT wearing a black hat!
He is doing this ONLY for a good reason: to secure and that is why CEH blong to the white hat and not to the black hat.
Hope that I explained it well.
If you have more questions about it.. feel free to ask :D
