Are there people who don't have .NET 3.5 installed?

I'm planning to write a utility in C# for Heroes 5 – a battle simulator and a database for creatures, heroes, and skills. Of course, forcing people to download frameworks would be cruel, but I'd like to use some features from the latest versions.
This leads to the following question: are there people who don't have the latest versions of .NET (3.5, 4.0, 4.5) installed? Which version should I target?
Please don't suggest the option "forget about everything and write it in Delphi" =-)