Random Text 4

private string GenerateRandomString(int size)
{
    Random r = new Random();
    string legalChars = "1234567890";
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < size; i++)
        sb.Append(legalChars.Substring(r.Next(0, legalChars.Length - 1), 1));
    return sb.ToString();
}

private void button1_Click(object sender, EventArgs e)
{
     MessageBox.Show(GenerateRandomString(6));
}