Why does the .NET runtime add underscores to my string?

I store my application settings the C# way (Properties.Settings.Default.Save();). The settings are then stored by the C# runtime in the folder:

C:\Users\UserName\AppData\Local\My_Company_Name

The strange thing is that I entered "My Company Name" as the Company-property in Visual Studio ([assembly: AssemblyCompany("My Company Name")]).

So, where do the underscores come from? I've seen other apps creating folders with blanks...