Random string c# static method and its enum

RandomStringHelper.cs

// Use it like:
// RandomStringHelper.RandomString(32, EnumRandomStringType.AlphaNumericWithSymbols);
// and it should return a string like "nd#9ian@iddjhn*And08183Anqov3a8Z"
public class RandomStringHelper
{
  private enum EnumRandomStringType
  {
      AlphaNumeric = 1,
      Numbers = 2,
      Letters = 3,
      Symbols = 4,
      AlphaNumericWithSymbols = 5,
      NumbersWithSymbols = 6,
      LettersWithSymbols = 7,
  }
  
  public static string RandomString(int length, EnumRandomStringType type = EnumRandomStringType.AlphaNumeric)
  {
      var st = string.Empty;
      var arr = "".ToCharArray();
      const string abc = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJLKMNOPQRSTUVWXYZ";
      const string num = "0123456789";
      const string sym = "~!@#$*";
      switch(type)
      {
           case EnumRandomStringType.AlphaNumeric:
              arr = (abc + num).ToCharArray();
           break;
           case EnumRandomStringType.Letters:
              arr = abc.ToCharArray();
           break;
           case EnumRandomStringType.Numbers:
              arr = num.ToCharArray();
           break;
           case EnumRandomStringType.Symbols:
              arr = sym.ToCharArray();
           break;
           case EnumRandomStringType.LettersWithSymbols:
              arr = (abc + sym).ToCharArray();
           break;
          case EnumRandomStringType.NumbersWithSymbols:
              arr = (num + sym).ToCharArray();
          break;
          case EnumRandomStringType.AlphaNumericWithSymbols:
              arr = (abc + num + sym).ToCharArray();
          break;
      }
      var random = new Random();
      for(var i = 0;i < length; i++)
      {
          st += arr[random.Next(0, arr.Length)];
      }
      return st;
  }
}