An Israeli advertising agency has been serving millions of online adverts that allow “zero-click” spyware to be used against targets, researchers at a Canadian university have said.

Citizen Lab, a digital investigations research unit at the University of Toronto, said it believed dozens of devices at the Qatari broadcaster Al Jazeera had been compromised by spyware delivered through ads run by Discover-Tech, which describes itself as a specialised digital advertising agency.