Dont share it!! Hide it somewhere so that none could find your dll.
You may use internal access specifier but since you said its a class library you definitely need to expose some of your classes as Public, so if someone referring the dll can access what ever the data you declared as public.
but if the classes are used inside a dll (class library) you can use define the class as internal
eg:
internal class MyClass
{
internal bool CanYouSeeMe
{
get;
set;
}
}
Read more about Access Specifiers in C# @
MSDN[
^]