[visual-studio] Why does the Visual Studio editor show dots in blank spaces?

I have a strange bug in the Visual Studio text editor. All my blank spaces are replaced by a "."

public class Person
{
  int age;
}

looks like this

public..class..Person..........................
{..................
..int age;...................
}.....................

I reset the settings to default. Didn't work. I also re-installed VS2008. Still didn't work. What's the error?

The answer is

Visual Studio is configured to show whitespace.

Press Ctrl+R, Ctrl+W.

If you are using C# keyboard mappings: (thanks Simeon)

Press Ctrl+E, S.

If you want to use the menu: (thanks angularsen)

Edit > Advanced > View White Space