Armed with laptops and smartphones, some 500 members of the Nahdlatul Ulama (NU) - one of the world's biggest Muslim organisations - are seeking to counter the Islamic State group's extremist messages.
"We'll never let Islam be hijacked by fools who embrace hate in their heart," tweeted Syafi' Ali, a prominent member of the NU's online army, a typical message to his tens of thousands of followers.
They are trying to hit back at IS's sophisticated Internet operations, which have been credited with attracting huge numbers from around the world to their cause.
The dangers of the growing IS influence in Indonesia were starkly illustrated in January when militants linked to the jihadists launched a gun and suicide bombing attack in Jakarta, leaving four assailants and four civilians dead.
Also Read
It was the first major attack in Indonesia for seven years, following a string of Islamic militant bombings in the early 2000s that killed hundreds.
As well as firing off tweets, the NU members have sought to dominate cyberspace by establishing websites promoting the group's moderate views, an Android app and web-based TV channels, whose broadcasts include sermons by moderate preachers.
But it will be an uphill battle and the NU, which has been promoting moderate Islam for decades, conceded they have previously struggled to take on IS's hate-filled messages.
"NU has for a while wrestled with this radical propaganda," said Yahya Cholil Staquf, secretary general of the NU, which claims at least 40 million followers.
The online drive comes as the NU is set to take its campaign to promote their tolerant form of Islam onto the international stage this week, with a two-day meeting from tomorrow of moderate religious leaders from around the world.
They aim to showcase their particular brand of the Muslim faith, known as "Islam Nusantara", to counter the IS jihadists' radical interpretation of Islam.
Meaning "Islam of the Archipelago" - Indonesia is the world's biggest archipelago, comprising over 17,000 islands - it is accepting of diversity and stresses non-violence.