With inputs from a small group of cyber jihadi hunters, which included former members of the hacktivist group Anonymous, the FBI had foiled over 10 terror plots and identified scores of ISIS recruiters and websites.
Their mission has acquired added urgency following the Paris attacks.
''We felt enough wasn't being done, so we wanted to put our skills to good use,'' said the executive director of Ghost Security Group, who only goes by the online hacker name DigitaShadow after numerous ISIS death threats, govtech.com reported. ''We're completely independent. We survive off donations alone.''
According to Michael S Smith II, co-founder of defence contractor Kronos Advisory and a former adviser to a Congressional terrorism task force, Ghost Security Group had provided valuable information since June.
He added, he became the de facto middleman between the hackers and the FBI after, the members of the group approached him. They learned about him from a newspaper article about cyber terrorism earlier this year and called for help because as they were not sure whether their data was getting through the FBI's tip line.
''When they first reached out, I wasn't sure if they were just enthusiastic people who wanted to help,'' Smith said. ''I was soon pleasantly surprised.''
"Without a doubt, this group has saved lives. At least into the dozens," Smith told CNNMoney. "There are people working in the national security community in the United States, Europe, the Middle East ... who will never be credited with that."
According to FBI director James Comey, the use of social media by ISIS was unprecedented in terms of how aggressively it engaged with people in the West.
Its members were essentially overwhelming the system, according to Smith, which meant there was room for outside support from groups like Global Security.
But for these friendly groups to be effective, they have to coordinate with those who "have the mandates ... to find, finish and fix the enemy," said Smith.