Ad blockers might seem like an unlikely defense in the fight against spyware, but new reporting casts fresh light on how spyware makers are weaponizing online ads to allow governments to conduct surveillance.

Spyware makers are reportedly capable of locating and stealthily infecting specific targets with spyware using banner ads.

One of the startups that worked on an ad-based spyware infection system is Intellexa, a European company that develops the Predator spyware. Predator is able to access the full contents of a target’s phone in real time.

Delivering malware through malicious ads, often referred to as malvertising, works by injecting malicious code into the ads displayed on websites on computer and phone browsers. Much of these attacks rely on some interaction with the victim, such as tapping a link or opening a malicious file.