Generate five digit Random Number

public string GetRandomString(int seed)
    {
        //use the following string to control your set of alphabetic characters to choose from
        //for example, you could include uppercase too
        const string alphabet = "abcdefghijklmnopqrstuvwxyz";

        // Random is not truly random,
        // so we try to encourage better randomness by always changing the seed value
        Random rnd = new Random((seed + DateTime.Now.Millisecond));

        // basic 5 digit random number
        string result = rnd.Next(10000, 99999).ToString();

        // single random character in ascii range a-z
        string alphaChar = alphabet.Substring(rnd.Next(0, alphabet.Length-1),1);

        // random position to put the alpha character
        int replacementIndex = rnd.Next(0, (result.Length - 1));
        result = result.Remove(replacementIndex, 1).Insert(replacementIndex, alphaChar);

        return result;
    }