What would it mean to have a stripped down social network that was also secure? It would look like Tuenti, the social network out of Spain. To give an example of how seriously they take security, the Tuenti API is closed because "of our efforts to be the most private, secure social network on the market..." But if you play nice, they can make exceptions for commercial apps and games they have tested.
Judging from their blog, Tuenti just keeps rolling out the features fast. Version 3.0 for Android has just been released, complete with the ability to share photos fast right from your photo library, along with photos created in group chats, and it also provides a simpler notifications center. Further SMS invitations are free; you can invite contacts to join Tuenti through SMS without SMS fees.
On this network, you can classify people as either friends (with whom you share) or contacts (who you can chat with). Their motto is: "Chat with everyone, share only with your friends." There are also different types of posts, moments and personal space. Moments can be photos or text limited to 140 characters. Personal space is a blog shared with friends.