Imagine: You’re happily browsing the internet one day when a host of urgent pop-ups tells you that malicious software has been discovered on your computer. These messages urge you to download software right away to fix the problem.

If you pay for and download the software, the program tells you that your problems are fixed. The reality: there was nothing to fix. And what’s worse, the program now installed on your computer could be harmful.

These programs are called “scareware” because they exploit a person’s fear of online viruses and security threats. The scam has many variations:

• You may get ads that promise to delete viruses or spyware, protect privacy, improve computer function, remove harmful files, or clean your registry.
• You may get “alerts” about malicious software or illegal pornography on your computer.
• You may be offered a free security scan. Inevitably, it will find a host of problems.
• You could get pop-ups that claim your security software is out-of-date, and your computer is in immediate danger.
• You may suddenly encounter an unfamiliar website that claims to have performed a security scan and prompts you to download new software.

If you’re faced with any of the warning signs of a scareware scam, shut down your browser. Don’t click “No” or “Cancel,” or even the “x” at the top right corner of the window. Some scareware is designed so that any of those buttons could activate the program. If you use Windows, press Ctrl + Alt + Delete to open your Task Manager, then click “End Task.” If you use a Mac, press Command + Option + Q + Esc to “Force Quit.”

If the problems continue, you may already have malware on your computer. There are steps you can take to get rid of malware.

And the best way to avoid these scams? Keep your computer security software up-to-date and make these other computer security practices part of your online routine.