Supporters of the Islamic State group are using the Internet Archive to frustrate efforts to delete their online propaganda, a study suggests, BBCreports.
The report analysed hundreds of thousands of links posted to two hidden forums used by the extremist group.
Archive.org links were found to be the most common type on both of the forums for the past two years.
The US-based service allows users to save and visit pages that might otherwise have been lost from the net.
A spokesman for the Internet Archive said it was taking steps to address the issue.