Are self-signed SSL certificates now valid?

Question

Windows

The wup.exe virus flew onto the PC, which did not want to be deleted. I installed ESET NOD32 Internet Security and cleaned the virus. And here I am trying to go to my site raised on nginx. I look at the certificate and see in the certification path instead of Let's Encrypt Authority X3 - ESET SSL Filter CA. What it is? It turns out that I can issue an SSL certificate myself and it will get into this storage and will display a green padlock in the browser?!
Please explain what it is!

Answer 1

What it is? It turns out that I can issue an SSL certificate myself and it will get into this storage and will display a green padlock in the browser?!

This is a certificate from ESET, you installed it yourself when you installed nod32 (so to speak, an evil woodpecker to yourself). Purely for yourself, you can generate a certificate and add yourself as a trusted publisher, it will work on your computer. On others it will not be until you add it with your hands

Answer 2

This is the ESET root certificate, it was most likely installed by Uncle Nod (Danya, don't laugh, there is such a surname). Now any certificate issued by this CA (nodovsky) will be valid on your computer. You can remove it from the "Trusted Root Certificates" store) - then all certificates issued by him will no longer be valid, but Uncle Nod may also stop working.
Why is it for him? Thus, it intercepts SSL traffic, local MitM

Answer 3

Are self-signed SSL certificates now valid?

Self-signed is no different from all the others.
The validity of a certificate depends on the trust in the person who signed it. If you trust, then it is valid, otherwise not.
See what certificates and root certification authorities you have trusted.