The spy can gain an implication from the public information, which also means they can manipulate a public as it is just an inverse way of the information flow.
The open information is not equally availed by the general public, but we basically screen out an information or obtain it from the popular source. If its nature is cracked, the spy can leverage it to manipulate the general public.
It is easy for the spy to send a faked intel or to guide their favored information through the net which is becoming a primary source of the information. For example, even the WIKI is availed for the information manipulation. The apparent lie cannot be accepted by them, but the well-designed faked information is hard to be detected. Or, the intelligence agency has selected an information available to the public, which can be useful for the manipulation as well.
The spy basically can manipulate many sites on the internet. The credibility and availability of each site are not equal, hence the spy should leverage their internet analysis to choose an appropriate way to spread an intel.
This methodology is applicable to the internet search. It is based on the algorithm, which is cracked to manipulate what shows up on the top of the lists. There are corporations for that matter, but the spy definitely has their own capability to leverage. If they can control a searching result, they do not just manipulate the target, but also change a direction of the mass as well.
For example, when the spy has manipulated a target to create a big social problem, such as a mass murder, there is a possibility that their involvement might be suspected. If its possibility is raised, they can send a counter-intel to lead the general public away from the truth. This is more like controlled through the traditional media, but the internet is also availed as a supplement.
There are many methodologies that they have accumulated internally for this manipulative operation. For example, one information is spread to multiple places, you just assume there are many facts to confirm it is a correct information.
Looking at the detail, it is basically the same source or wording, but the human being has a tendency to assume the credibility is high when seeing it at many locations. This kind of the internet manipulation can be conducted by the private investigator as well.
In any way, if there is a way to gather information, there is a way to manipulate it inversely. The information gathering and operation are always a twin of the intelligence job, which holds true to the open information.