According to an official in charge of the country's new electoral commission for the 1994 election, an unknown hacker managed to penetrate their computer system and up the share of the vote for three parties.
Among the parties who benefited were the National Party, which had led South Africa from 1984, whose vote share increased by around three per cent and the right-wing Freedom Front party which saw its vote share pushed up by between 2.5 per cent and four per cent.
The Inkatha Freedom Party, whose mainly Zulu supporters refused to ally themselves with the ANC and were involved in violent clashes with Mandela's African National Congress party supporters, saw its share of the vote increase between four and five per cent.
The revelation was made by former electoral commission official Peter Harris in a new book entitled Birth: The Conspiracy to Stop the '94 Election, which is serialised in South Africa's Sunday Times newspaper.
He told how the delay caused by the voting sabotage – whose authors and motives were never discovered – almost tipped the country over into widespread violence as the poll results trickled in painfully slowly.
"The hacker went in between 05:56 and 06:41 on the morning of 3 May and made changes to the vote count of three parties," he quoted a forensic investigator as saying in his book.
Recalling the turmoil of the country at the time, he wrote about people rushing to stock up on foodstuffs and of farmers clustering in fear of being driven off their land by black militias.
Rumours abounded about a right wing, military-backed coup, the declaration by the standing government of martial law and a total recasting of the election eight months later.
"The frozen election results place the country in limbo," he wrote. "Fear feeds on fear and the political mercury rises. The spooks tell us that security forces have been placed on high alert."
In the end, the tampering was not able to change the overwhelming support for Mr Mandela's ANC.
When the final results were announced on May 6, the ANC had won 62.6 per cent of the vote, the National Party 20.4 per cent and the IFP 10.5 per cent.
Mr Mandela, released in 1990 after 27 years in apartheid jail, was sworn in as president four days later. The book is due to be released next month.
