Spokesman Sershan Naidoo said the recordings were of a top level discussion that took place in 2009 about an internal security breach by lottery operator Gidani.
A Gidani IT manager was caught defrauding the lottery of R250,000 by duplicating winning tickets and stealing unclaimed winnings. A criminal case had been brought against him.
Naidoo said recordings of the board meeting were leaked to Media 24, which ran the story online on Monday.
News 24 reported that the tapes showed confusion among top management as it grappled with the fraud.
The website reported that NLB CEO Vevek Ram described on the tapes how a whistelblower had told Gidani CEO Bongani Khumalo that "something was going on".
Gidani then arranged for surveillance of the man.
"Had the whistleblower not come forward, this fraud would be continuing as we speak," Ram reportedly said on the tapes.
The recordings apparently include the board's debate on how to punish Gidani and whether its licence should be revoked.
Now, with tapes of that meeting made public, the board was again questioning its security protocols.
"Such a devious act can only be seen as a vendetta against the board, the department of trade and industry and the lottery operator by someone seeking to bring the integrity of the National Lottery to disrepute," board chairman Alfred Nevhutanda said in a statement on Tuesday.
That person might even work for one of the consortia which would bid for the next lottery licence, he said.
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