A user reports experiencing an excessive number of pop-up ads that occur even when the browser is not open. This behavior is accompanied by sluggish system performance. As a technician, what is the FIRST step you should take to address this issue?
Run a full system anti-malware scan with an updated anti-malware tool.
Clear the browser's cache and cookies.
Install a pop-up blocker extension on the user's web browser.
Reinstall the operating system.