This study investigates the evolving challenges intelligence and law enforcement agencies face in countering Salafi jihadist terrorist activities across digital platforms, focusing on integrating artificial intelligence (AI) and data fusion technologies in open-source intelligence (OSINT) methodologies. Through an analysis of case studies involving ISIS and other non-state actors, the study examines how terrorist organisations adapt their digital strategies to evade detection while exploiting social media platforms, instant messaging applications and websites for recruitment, propaganda, and operational planning. The study demonstrates the necessity of developing advanced technological solutions such as the integration of AI-enhanced OSINT capabilities, combined with data fusion approaches, that can improve analysts’ ability to process multilingual content, identify threat actors who use online anonymity, and detect patterns of terrorist activity across multiple network layers. However, the study also reveals critical ethical and operational challenges in balancing effective counter-terrorism measures with privacy rights and civil liberties. The study concludes that while OSINT, AI and data fusion tools can substantially augment human analysis capabilities, successful counter-terrorism efforts require a carefully calibrated approach combining technological innovation and human expertise.