The expose released on Tuesday and published by several major international media outlets, like Le Monde in France, The Guardian in Britain, Ming Pao in Hong Kong was the result of a six-month investigation cloaked in high secrecy by the nonprofit organization.
It came out of a cache of 2.5 million files on private offshore banking accounts that could be used for tax evasion.
The files were leaked to the ICIJ, and last April, after a 15 month investigation, the group began to release stories about the "who's who" of the world hiding their assets offshore.
It is a huge achievement for the small consortium of member journalists in more than 60 countries.
To deal with the Chinese case, the group took the same tack it has used with other stories. It linked up with a dozen media organizations around the world to give its scoops maximum visibility and ease the burden, it says, on the traditional media.
"We feel the mainstream media is not spending the kind of time that they used to spend on long-term investigative reporting," said Gerard Ryle, a former investigative journalist in Australia who became head of the ICIJ's headquarters staff in September 2011.
Ryle, in an interview, said major newspapers, struggling with slumping circulations and advertising revenues, are reluctant to finance in-depth investigations in fear of risking coming up empty-handed with a story or "taking on powerful people who are willing to fight back."
The 'luxury' of time
Working in small, unpretentious offices not far from the White House, ICIJ employees and freelancers are not immune to such pressures.
But they have a precious asset: time to spend on stories that need it.
"It's one luxury we have here," Ryle said.
To conduct its investigation of the Chinese files, the consortium gathered a group of journalists in July in Hong Kong and taught some of them encryption techniques to be able to work under the radar of Beijing's surveillance.
"We couldn't do it so complexly that it would discourage journalists from participating," Marina Walker Guevara, ICIJ's deputy director, explained to AFP.
Then the journalists had to recover and verify the data in a list of 40,000 names, a "boring and painstaking" task, said the Argentine journalist.
"People think that investigative journalism is glamorous, but it's not," she added.
The ICIJ also had to overcome cultural and language barriers among the journalists, as well as the withdrawal of a Chinese media outlet from the project in November after being warned by authorities in Beijing.
"We don't know exactly how they became aware of our investigation, maybe online surveillance. Who knows?" Walker Guevara said.
These setbacks failed to soften the impact of the group's revelations about the offshore holdings of China's political elite, including the brother-in-law of President Xi Jinping.
In retaliation, Chinese authorities blocked access to the ICIJ website on Wednesday, as well as the websites of the other media that had worked on the project. The pushback was expected, although this time the scope of the targets was slightly different.
"It's been interesting to see the reaction of the Chinese authorities," Walker Guevara said.
"In the past they have had to deal with a similar situation but it was only with one media organization. Now they were scrambling to block 10 different websites."
At a time of an industry-wide crisis, the partnership between the traditional news media and ICIJ could spell a brighter future, said Brant Houston, a journalism professor at the University of Illinois.
"You now need a global network to pursue investigative stories in a globalized economy. The nonprofit organistions can afford (it) but do not have the distribution channels of the mass media," he told AFP.