private static bool ValidateCardNumber( string cardNumber )
{
    try
    {
        // Array to contain individual numbers

        System.Collections.ArrayList CheckNumbers = new ArrayList();
        // So, get length of card

        int CardLength = cardNumber.Length;

        // Double the value of alternate digits, starting with the second digit

        // from the right, i.e. back to front.

        // Loop through starting at the end

        for (int i = CardLength-2; i >= 0; i = i - 2)
        {
            // Now read the contents at each index, this

            // can then be stored as an array of integers


            // Double the number returned

            CheckNumbers.Add( Int32.Parse(cardNumber[i].ToString())*2 );
        }

        int CheckSum = 0;    // Will hold the total sum of all checksum digits


        // Second stage, add separate digits of all products

        for (int iCount = 0; iCount <= CheckNumbers.Count-1; iCount++)
        {
            int _count = 0;    // will hold the sum of the digits


            // determine if current number has more than one digit

            if ((int)CheckNumbers[iCount] > 9)
            {
                int _numLength = ((int)CheckNumbers[iCount]).ToString().Length;
                // add count to each digit

                for (int x = 0; x < _numLength; x++)
                {
                    _count = _count + Int32.Parse(
                          ((int)CheckNumbers[iCount]).ToString()[x].ToString() );
                }
            }
            else
            {
                // single digit, just add it by itself

                _count = (int)CheckNumbers[iCount];
            }
            CheckSum = CheckSum + _count;    // add sum to the total sum

        }
        // Stage 3, add the unaffected digits

        // Add all the digits that we didn't double still starting from the

        // right but this time we'll start from the rightmost number with

        // alternating digits

        int OriginalSum = 0;
        for (int y = CardLength-1; y >= 0; y = y - 2)
        {
            OriginalSum = OriginalSum + Int32.Parse(cardNumber[y].ToString());
        }

        // Perform the final calculation, if the sum Mod 10 results in 0 then

        // it's valid, otherwise its false.

        return (((OriginalSum+CheckSum)%10)==0);
    }
    catch
    {
        return false;
    }
}