Dr Mahathir Mohamad is on the warpath against Prime Minister Najib Abdul Razak but chose to be diplomatic in his trademark cynical manner when quizzed on the latter's jab at him earlier this morning.

"Good luck to him. I wish him well," the former premier told reporters at the sidelines of a forum in Kuala Lumpur.

He was responding to Najib's speech at InvestMalaysia 2015 today, where the prime minister took a swipe at Mahathir's claim of being alone in seeking the truth.

During his speech at the social media forum earlier, the doctor-turned-politician spoke on various issues ranging from calling for a change in leadership, pornography and teenagers growing new "appendages"

Mahathir said it was too easy to access "filth" online, which could corrupt young Malaysians.

"A child as young as 3-years-old could type 'sex' and get all this dirt.

"They would grow up with all this filth and this would not be good for society," he added.

Teens easily excitable by porn

This he said, leads to sexual crimes, as children, especially teenagers who have "grown new appendages" are easily excitable by pornography.

"We have a lot of sex crimes, we find people abusing even little children, even old ladies, why, because they are excited [...] whatever comes their way they will try things out," he said.

Besides this, he said the internet can also be used to learn about dangerous things like making bombs, and as such should be censored.

"Censorship of social media is needed, not to block out chedet.cc, that one please don't block, but to block all this filth that comes out of (the internet)," he said.

On his own use of social media, Mahathir said he found it very useful to irritate people.

Irritate a lot of people

"When I ceased to be prime minister, I found that social media is a good way for me to irritate a lot of people," he said drawing roaring laughter from the crowd.

Mahathir has been using his blog extensively as his main platform to launch attacks against Najib.

However he stressed that writings online should be based on fact, and not rumours, warning that social media can be used for good or evil.

"Social media is like a knife [...] with a knife you can carve a beautiful object, you can also stab someone and kill him," he said.

Meanwhile on the Sedition Act, Mahathir said it is a good law, but there was a tendency to abuse it.

"The sedition act is a good act if it is directed at sedition [...] (but) there is a tendency to abuse the law.

"The act is there to stop people from saying this country should have a civil war and overthrow the government, that is sedition.

"But if we say the government is not doing to well, we need a change of leader, that is not sedition," he said, wondering outloud if he was talking about himself, drawing more laughter from the audience.