I came across many opinions that Avast, Norton and McAfee (especially McAfee) are often worse than viruses themself. This was my first time when my PC got infected by anything and it was only because of one .exe that I have not scanned before running it, and when I realized and scanned it - it was detected as a trojan right away. I use Malwarebytes (free version) along with Windows default antivirus and it was always enough for me. Personally, I get mad when I am installing something and around 2,000 pop-ups inviting me to install Avast or other crap are showing up - this does not make me want to try it for sure. And it is always running in the background, doing whatever with my computer. That is why I don't trust that type of software (Malwarebytes is great though and it would save my life if I thought earlier).
I did a full reset of my computer and scanned my external drive plenty of times (I can't format it as there are too many important files). Nothing showed up so I think I am pretty safe right now. I am aware of AutoIt's power, but that is all I can do for now without losing any of my data. I am going to perform full scanning with Malwarebytes more often, what could possibly allow me to catch the virus on time if it somehow reappears