I was speaking tonight to Rav Grananstien of Mishmeres Stam in Benai Brak. He was telling me about a new "fingerprint" program they have for tefillin and mezuzos where once it is scanned in the computer it automatically goes on a database and if the tefillin are rescanned years later the program can identify who's they are and where they come from, like a fingerprint.
Then he told me that sometimes they do computer checking for sochrim and X amount of mezuzos and tefillin will register spelling mistakes. So the sochrim give it back to the sofrim and get credits etc or replacements. He says it happens once in a while that they scan mezuzos / parshiyos and the computer recognizes the mezuzos / parshiyos ie it has seen it before, and previously it had a spelling mistakes but it has now come back without a mistake, meaning, chalilah, the sofer is not a yiras shomayim and has corrected the mistake without realizing that the fingerprint program will pick up on it!
I asked the Rav how often it happens and he said at least 4 or 5 sofrim have been caught out since they started the new program.