scareware
Scareware is a real potential threat in cyberspace. When scareware is used, the user is made to believe that his personal computer is defective or otherwise malfunctioning. In doing so, the functioning of the computer is impaired by a malicious program of the cyber criminals. The user himself downloads the corresponding malware from the website of the cyber criminals.
The online criminals' modus operandi is as follows: They send spam emails with an interesting reference to a website where something can be viewed or downloaded for free. The website is prepared in such a way that the visitor downloads the malicious program. This way, the malicious program gets onto the user's computer where it causes operational disruptions. This may be reflected in the computer's performance or in strange error messages.
This is the approach for online criminals who sell the affected user an antivirus program that improves the performance again and pretend the user that he has received the right help with the purchased program.