Evil is a proof-of-concept site -- it does something shocking to prove to how easy it is for someone with truly malicious intent to perform the same action. In this case, the software searches for public groups that serve the purpose described above and harvests the names, pictures, and phone numbers of everyone in the groups. In English: it shows how easy it is to collect people's private phone numbers from Facebook groups. Given that this site is just meant to teach, it redacts the last digits of the phone numbers, but if you'd like to get a clearer picture of what we're talking about, check this out. Scary, huh?
I shudder to think of what will happen when marketers figure this out -- text-message SPAM, anyone?