What is the threat
Phone calls during which callers attempt to convince you to give them access to your computer. If you do as they request they may steal information from your computer or infect it with ransomware or other malware.
How does it work
You receive an unsolicited phone call from a person identifying themselves as being with Microsoft or from a Microsoft Partner or some other official sounding security company. The caller will claim a virus has been found on your computer (or multiple viruses) and they will offer to fix it for you. They may direct you to a website to download a file or give you specific instructions which will give them remote control over your computer.
Once the caller has access to your computer they will steal personal or financial information, install viruses, malware or ransomware.
Why do they do this
There can be multiple reasons for the scam. In some cases the caller will search your computer for credit card numbers, banking or other financial information and steal that information for their own use. Another purpose is to install ransomware on your computer. Ransomware is a program which will lock all your files so your computer is essentially rendered useless. The caller then forces you pay a ransom for them to unlock the files. Once a computer is locked with ransomware it is very difficult (if not impossible) to clean off the ransomware or unlock the files without the specific codes known only by the scammer. The caller also may install programming on your computer which allows them to use it as a slave. They can later use your computer (and you may not even notice) to send out spam emails or they may use it in combination with other computers they control to attack websites.
How do you know it is a scam phone call
No legitimate company will make such a call to you. In fact, neither Microsoft nor any other company has any way of knowing if there is a virus on your computer.
What should you do
If you receive a call of this type...HANG UP IMMEDIATELY!
What happens next
Usually nothing. The scammer will simply forget about you and go on to the next name on their list. They are working from a telephone book or other phone listing. They have not targeted you specifically. You were just a name and number on a list.