Create a hash (aka password) of a fixed size, using one number, ony symbol, one upper letter and many lower letters

Hash.cs

const String Letters = "abcdefghijklymnopqrstuwxyz"; //bota o resto ai
const String Numbers = "0123456789";
const String Symbols = "@$!?"; //põe mais se quiser
const Int32 Size = 10;

public static String CreatePassword()
{
    var random = new Random();
    var password = new StringBuilder(Size);
    var upperUsed = false;
    var numberUsed = false;
    var symbolUsed = false;

    for (var i = 0; i <= Size; i++)
    {
        var rand = random.Next(1, Size);
        switch (rand)
        {
            case 1:
                if (upperUsed)
                    break;
                password.Append(Letters[random.Next(0, Letters.Length)].ToString().ToUpper());
                upperUsed = true;
                continue;
            case 2:
                if (numberUsed)
                    break;
                password.Append(Numbers[random.Next(0, Numbers.Length)]);
                numberUsed = true;
                continue;
            case 3:
                if (symbolUsed)
                    break;
                password.Append(Symbols[random.Next(0, Symbols.Length)]);
                symbolUsed = true;
                continue;
        }
        password.Append(Letters[random.Next(0, Letters.Length)]);
        if (i < Size)
            continue;
        if (!symbolUsed || !numberUsed || !upperUsed) //não usou os caracteres obrigatórios, começa de novo
        {
            password.Clear();
            i = 0;
        }
    }
    return password.ToString();
}