Tessa brought me her laptop after something frightening happened on the screen. Suddenly, it filled with warnings claiming that her computer was infected and telling her to call a support number immediately.

It looked serious. It was designed to.

Tessa was concerned enough that she actually started to call the number shown on the screen, but fortunately she hung up before the conversation went any further.

That was important. The fake warnings themselves were mostly designed to scare her. The much greater danger would have started if someone on the other end had convinced her to install remote-access software, hand over passwords, provide payment information, or let them “fix” the computer.

That is why I tell clients: never call a phone number that suddenly appears in a virus warning, browser pop-up, or security message. Microsoft, your antivirus company, and your bank are not going to lock your screen and demand that you call an unfamiliar support number.

What made Tessa’s computer worth examining was that there were still several unwanted changes behind those warnings. Her antivirus protection was not doing the job she thought it was doing. The browsers contained unwanted extensions with broad permissions, another browser had effectively taken over part of her normal browsing experience, and an untrusted website had been allowed to send notifications that repeatedly claimed she had a virus.

Eventually those warnings became overwhelming and filled the screen with fake security messages. They looked dangerous, but the messages themselves had not damaged the computer.

I removed the unwanted browser software, extensions, and notification permissions and then checked the system again. The frightening warnings were gone, and there was no evidence that someone was actively controlling the laptop.

Tessa did one of the most important things she could have done: she hung up. When a warning tells you to call immediately, that urgency is often the trap.

Related service: Virus Removal & Computer Security.