Vicious. That was how Indonesian President Joko Widodo described social media users in his country who, in recent years, have taken to the Internet to propagate hate speech, slander and fake news.

He should know. After all, the President, popularly known as Jokowi, is often the subject of Internet memes accusing him of being a communist, or implying that he is Chinese or Christian, and not a pure Muslim.

"I was asked, 'President Jokowi, how is the state of social media in Indonesia?', I replied, 'In Indonesia, it can get very vicious'," said Mr Joko in a Facebook post on Tuesday.

The online smear campaign against Mr Joko emerged in 2014 when he was running for the presidency against former army general Prabowo Subianto.

But the issue of fake news really came to bear late last year when former Jakarta governor Basuki Tjahaja Purnama, who goes by his Chinese nickname Ahok, was accused of and later charged with blasphemy against Islam.

As a minority Christian politician, it was no surprise that Basuki - who was running for re-election as governor - was frequently depicted in Internet memes or fake news, which were focused on his race and religion, to stir public dissent against him.

Last month, a police investigation confirmed what many had suspected all along - that such vitriol on the Internet was part of an organised campaign by a "fake news factory" against political targets.

The online syndicate known as Saracen allegedly charges tens of millions of rupiah to publish and spread fake news, as well as hate speech against a person or persons, said the police.

The going rate for a quick "buzz" of customised fake news online is 75 million rupiah (S$7,600).

Investigators said last week that they have established a money trail between members of Saracen and a handful of people with links to street protests against Basuki.

They said that with help from Indonesia's anti-money laundering agency PPATK, the police have identified 14 bank accounts used by the group to receive payments from their clients.

Saracen is led by a 32-year-old Pekanbaru resident identified by the police as Jasriadi.

The police have been deliberately vague with details of the case as investigations are still ongoing, but Jasriadi had said publicly that he is a supporter of Mr Prabowo.

Police spokesman Martinus Sitompul said on Tuesday that based on preliminary investigations, Jasriadi pockets about 10 million rupiah of the 75 million rupiah, with the rest of the money used for setting up an online site, and hiring so called "journalists".

"The 'journalists' will then write up articles with content directed by clients, and use media platforms such as the Facebook group pages of Saracen news, Saracen Cyber Team, saracennews.com site, and various other groups that will attract netizens to follow," he added.

So far, five suspects, including Jasriadi, have been arrested as part of the investigation into the syndicate that runs a news site and a Facebook page which, at its peak, had some 800,000 followers.

The group is said to have also created several social media accounts for the sole purpose of spreading false information and hate-mongering, on behalf of "clients" during the anti-Ahok protests in Jakarta.

Basuki is now in jail, after being found guilty in May of insulting the Quran, just days after he lost the Jakarta gubernatorial election.

Before he was sent to prison, Basuki had also been the target of several attacks on social media, mainly by Muslim hardline groups such as the Islamic Defenders Front (FPI).

The resulting racial and religious tensions from the actions of the FPI in the run-up to the Jakarta election and Basuki's blasphemy trial, had raised concerns and threatened Indonesia's values of pluralism.

The police have not identified Saracen's clients but its website reportedly listed lawyer Eggi Sudjana and retired army general Ampi Tanudjiwa as its advisers.

Mr Eggi is widely known to be the lawyer of FPI leader Rizieq Shihab, who on Dec 2 last year staged one of the country's largest anti-Ahok protests.

The crackdown on Saracen began with the arrest of a 44-year-old Indonesian on July 21. Faizal Muhammad Tonong is said to be a coordinator in the Saracen network who, a day before his arrest, was caught uploading a meme of President Joko, accusing him of being anti-Islam and pro-communist, among others.

Some time between July and last month, Jasriadi and Saracen's West Java representative Sri Rahayu Ningsih, 32, and a man named Ropi Yastman, were picked up by police.

According to local news reports, Ropi is the administrator of a Facebook group that calls itself Keranda Jokowi-Ahok, or coffin of Jokowi- Ahok in English.

The police estimate there to be 800,000 Facebook accounts linked to Saracen. Jasriadi has disputed the number.

"I hacked a lot of accounts, but not 800,000, probably about 150,000," he told Tempo news. "We are Pak Prabowo's supporters, I hacked accounts (whose users) had crossed the line by attacking Islam and Pak Prabowo."

A major breakthrough came when police arrested on Sept 8 52-year-old Asma Dewi, who allegedly transferred 75 million rupiah to a Saracen member. Asma is a member of Tamasya Al-Maidah, an Islamic group that urged Muslims to gather in Jakarta to rally against Basuki during the gubernatorial election.

The police found at least four posts with anti-Chinese slurs on her Facebook page.

The Sunday Times understands that more suspects will be identified as investigations continue.

Despite the latest arrests, the Saracen news site remains online, to the surprise of many.

But Communications and Information Technology Minister Rudiantara, who like some Indonesians go by one name, said that it was not blocked intentionally, so as to facilitate police investigations.

"That is done after coordinating with the police, because part of their investigations is the Saracen site, not just Facebook," he added.