THE dark corners of cyberspace are being illuminated by indexing software that can reach into secretive websites that are normally inaccessible to search engines. This could allow search engines to cover online forums lurking within the “dark web”, and provide insights into what is being said by groups who would rather keep their conversations secret.

Conventional search engines use programs called spiders or web crawlers that scuttle around the internet and index what they find. However, many websites are protected by security restrictions that fend off such software. Screening out all traffic from IP addresses belonging to well-known search …