I have a Credit Card Number in a .xlsx file embedded in a Word document that is not being detected. The Credit Card Number has no dashes or spaces, just a 16 digit number.
MS Excel will, by default, only track 15 significant digits in a standard number cell, regardless of format and replace the rest with zeros! Space delimited and dash delimited CCNs work fine. With a straight 16 digit valid CCN number, Excel changed the last number to a 0. By changing the last digit to a 0, this is no longer a valid CCN and fails the Luhn check – Symantec DLP is working as designed and not picking it up to avoid a false positive.
Also see: MS article 269370