KNEC has downplayed reports that Mathematics Paper 1 and Chemistry Paper 1 which were administered on Monday had been leaked.
Prof George Magoha, KNEC chair, said that the council had confirmed that the papers that were doing rounds were not genuine.
Magoha said the fake papers did not have the slightest similarities to what had been set and printed.
"The council wishes to categorically reiterate that, like was the case in KCPE, no KCSE examination paper has been leaked whatsoever," Prof Magoha said in a statement.
"The security features of the ongoing examination are imitation-proof, high level and so sophisticated for anyone to copy," he said.
He said: "The public should be well notified that no exam has been leaked; no exam will be leaked,"
The KNEC chair warned parents against spending money to buy any papers offered for sale in the guise of being genuine KCSE tests.
Read:
"They (parents who buy exams from fraudsters) will be arrested since the government has assembled a network to avert cheating," Magoha said.
Magoha urged Kenyans to "stop falling prey to the clear con game being mounted by unscrupulous businessmen".
"They only want to take opportunity of the tough measures put in place to curb cheating to fleece innocent Kenyans," he said.
Magoha said those who buy the fake papers can only distract their children from the right preparations they have made for the examinations.
"They will blame themselves once they confirm that they were conned. We wish to urge candidates to remain focused as they continue to sit this most clean and credible KCSE examinations," he said.
He said as was the case of KCPE, the council had on Sunday received reports of people purporting to be selling genuine Mathematics Paper 1 and Chemistry Paper 1.
Also read:
KCSE is scheduled to end on November 30.