The government switched its stand on whistleblowers because the latter opened the wrong can of worms, said Dr Mahathir Mohamad.
He noted how the government once called for whistleblowers to be protected because it is good for society.
Mahathir said whistleblowers deter those in power from wrongdoing because they are able to expose "miscreants" to the due process of law.
"Then they whistleblowed over the wrongdoings of the head of government.
"Suddenly what was considered right became wrong. The whistleblowers must be investigated and punished.
"Don't they know they cannot whistleblow on the prime minister? Others yes. But not the prime minister," he added in his latest blog posting.
Mahathir was responding to investigations on those who leaked documents to the Wall Street Journal , which implicated Prime Minister Najib Abdul Razak.
Covering up is akin to abetment
Inspector-general of police Khalid Abu Bakar today confirmed that the police would investigate all relevant parties in relation to the allegation that three Bank Negara Malaysia (BNM) senior officers had leaked "sensitive documents" to the Wall Street Journal .
And although there is risk in whistleblowing, Mahathir pointed out that there is also risk in covering up evidence of crime, as well as aiding and abetting.
"You are really between the devil and the deep sea. You must make the decision now or forever regret," he said.
The Wall Street Journal , citing Malaysian government investigators had revealed that almost RM2.6 billion in 1MDB funds had been deposited into Najib's private bank accounts through proxies.
A special task force has since been established to probe the matter further.
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