I guess that my problem started after downloading a crack for a video format converter program. Although the site from which I downloaded the file is usually reliable, it may have contained a Trojan.
No one sent me a link or a suspicious email. I downloaded the file personally at my own risk. It was a big mistake for which I unfortunately paid dearly.
Dump windows asap. Windows itself is dangerous and a malware enabler.
Use a linux distribution. There are many free video edit/converter software in the linux ecosystem.
The era of cracks has ended long time ago. Never think they will give you the crack without taking away something precious from you.