Infected with "Powered by Provider"...

[REDACTED]

I installed Avast in my Dad's computer to fight this infection, did a full scan, which cleaned some stuff, but "Provider" wasn't cleaned; this adware only affects the internet browser.

Tried a scan with SpyHunter and came up with something called Zwiiky, which I don't know if it's real, but it's something else that Avast didn't pick-up. This wasn't cleaned either, because you need to pay and register the software.

Why isn't Avast detecting these infections?

[Eddy]

It can be that avast does detect it if you enable PUP scanning.
Keep in mind though that it is not possible for a anti-malware application to detect everything.

https://forum.avast.com/index.php?topic=53253.0

Zwiiky.com homepage got on your computer after you have installed a freeware software (video recording/streaming, download-managers or PDF creators) that had bundled into their installation this browser hijacker.

[REDACTED]

I understand it's not possible for Avast to get everything, specially the free version, but these particular malwares seem to be well known and I installed with the default settings, which I thought would get them.

[Eddy]

Free or not has nothing to do with it.
Both the free and the paid versions are using the same detection.

[Pondus]

I installed with the default settings, which I thought would get them.

PUP detection is default off in all scan except boot scan, so you need to turn it on if you want PUP detection

anyway a combination of Malwarebytes and AdwCleaner scan usually clear most of this crap

[REDACTED]

Alright, I'll check Avast's settings and download one of those malware fighters.

Thanks.

[Eddy]

I suggest you follow the instructions in the link I gave you.