Virus: PUP that injects scripts in each site that I visit

I left my cousin alone for 5 minutes and he managed to ruin my system.

I think it's a PUP that opens pop-ups to sites that benefit its creator.
Luckily I do not have any pop-ups. I think that's because of the built-in ad blocker I have in Opera. So I thought that I managed to eliminate the PUP (Deleting the Appdata folders and the Registry edition were involved)

However, I noticed that there were some codes that were being injected into the bottom of the Tag of any site that I visited.

A nice length

(Here it is:

And a

A GoogleAnalytics script.

I have run system scans in Malwarebytes, it goes without saying that nothing has been detected …

Any help to eliminate this problem is appreciated.