 Microsoft technical support calling, want to help you fix it. They get the victim to open up their computer. Inevitably, they somehow guide the victim into taking steps that reduces the security levels on the computer. And then once the door is sort of open, the attacker walks right in. At that point, the attacker takes over the computer. They can steal your passwords and personal information. How do they get their foot in the door? What will happen is the attacker will just reach out to a bunch of potential victims, maybe by phone.