Seems like an old-school [1]race condition:

     Citing arrest warrants, here's how The Hartford Courant said the
     Connecticut scheme worked:

     An investigator for the Connecticut Lottery determined that terminal
     operators could slow down their lottery machines by requesting a
     number of database reports or by entering several requests for
     lottery game tickets. While those reports were being processed, the
     operator could enter sales for 5 Card Cash tickets. Before the
     tickets would print, however, the operator could see on a screen if
     the tickets were instant winners. If tickets were not winners, the
     operator could cancel the sale before the tickets printed.

   Source: [2]Cops: Lottery terminal hack allowed suspects to print more
   winning tickets | Ars Technica
     __________________________________________________________________

   My original entry is here: [3]Cops: Lottery terminal hack allowed
   suspects to print more winning tickets | Ars Technica. It posted Mon,
   28 Mar 2016 14:49:46 +0000.
   Filed under: InfoSec, lottery, race condition,

References

   1. https://en.wikipedia.org/wiki/Race_condition
   2. http://arstechnica.com/security/2016/03/cops-lottery-terminal-hack-allowed-suspects-to-print-more-winning-tickets/
   3. https://www.prjorgensen.com/2016/03/28/cops-lottery-terminal-hack-allowed-suspects-to-print-more-winning-tickets-ars-technica/