What can malicious attackers do with pop-up advertisements?

Malicious attackers can indeed purchase ads through networks, which is a common tactic used in malicious advertising, often referred to as "malvertising." By buying ad space through legitimate ad networks, attackers can position malicious content within legitimate web pages. Once users click on these ads or even view them, they may be led to malicious websites or inadvertently download harmful software. This method allows attackers to reach a wide audience without needing to set up their own infrastructure, leveraging the existing systems of established ad networks.

Considering the other options, ensuring pop-ups always appear on a website involves manipulating the website itself, which is a different approach that doesn't solely rely on the use of advertising networks. Disabling browsers for security and encouraging updates to browsers are more geared towards browser functionality and user compliance rather than actions linked directly to pop-up advertisements by malicious actors. These actions may be outcomes or preventative measures but do not directly relate to the functionality and exploitation of advertising networks like purchasing ads does.