It's a surprise, though, to find that the OS ranked most secure is Ubuntu, an Open Source Linux platform.
This assessment has a personal side, for me. I just sent off some pre-configured laptops to be used in a Kenyan medical facility and NGO for children affected by HIV+: Nyumbani.org. And, what was delivered to them was, in fact, Ubuntu 12.04. I think anyone can agree that this organization deserves to be secure, at the lowest cost. But, to be able to meet the highest standard, at a zero-cost is a big win for everyone.