It is surprising to me how many of my customers are falling for this and similar scams. This or similar types of ads may pop up on your screen if you accidentally visit a dangerous site or click on the wrong link.
The idea behind this is to scare you into allowing the person at the number you call to take control of your computer and clean it from viruses, malware etc. The problem is that this is a trick. An easy way for the people on the other end to charge you for something that you do not even have. it is the psychology of fear.
If you get this or a similar popup, shut down your computer and call your computer repair or I.T. person (hopefully me) but either way, do not succumb to these scams. By doing so you are potentially allowing others to have access to critical information such as passwords and credit card numbers. THINK before you act!