"I have spent a lot of time in jail. I am not scared of jail, I have been there," said Zuma, who under apartheid was jailed for 10 years on Robben Island with Nelson Mandela.
During a speech to hundreds of Africa National Congress supporters in Dumbe, a small town in his Kwazulu-Natal province, Zuma accused the opposition of "using the courts to scare the ANC.
"We are not going to be intimidated," he said.
The watchdog's investigations focussed on accusations that Zuma had allowed the Guptas, a wealthy Indian business family, to have undue influence over government, including letting them choose some cabinet ministers.
The report prompted the opposition to schedule a no-confidence vote in parliament on November 10. Zuma has survived two such votes already this year.
Zuma, 74, has weathered a series of major scandals since coming to power in 2009, but rapidly declining support for the ANC has threatened his presidency.
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