Pirrit Virus on my Mac, need help removing, help.

Just like you have no capability to delete items from the Updates volume, no malware has the capability to write to that location.

Apple put that file there.

Avast just lied to you to make you think it is useful. Get rid of it.

In addition to the other answers: PUP means Potentially Unwanted Program.

After uninstalling Avast (just throwing it into the bin is not ok: follow Avast’s instructions how to uninstall) you can if you want download the free malwarebytes for Mac https://www.malwarebytes.com/ and let it run now and then

Uninstall AVAST. It is not needed. It may report false problems. It uses system resources while providing no benefit. It may cause issues.

Why would it actually lie about an adware?

It's a piece of software, it's neither honest nor dishonest. What is happening is that it's found something it doesn't recognise and flagged it. That's why you need to get rid of AVAST. It's just not competently programmed for Macs, reports false positives and can easily cause you to hose your OS installation or dataloss.

I tried Malwarebytes but it didn't detect ****

Because it recognises the file as valid, correctly.

The best thing that you can do for your Mac is completely uninstall Avast, and any other utilities that claim to "protect", "speed up", "optimize", etc. your Mac.

There are no known Windows-like Viruses in the wild that self replicate and affect macOS, because of the underling UNIX  Foundation and Permission Limitation. 

The Only thing this Antivirus software is protecting is the Bank Account of the Developers and for zero return to the User aside from the problems this software creates.

The The Built in Security  is all that is required to protect the computer.

Any of the below should be removed as per Developers Instructions 

Avast AntiVirus please. please read some of the posting about this specific Application.

There has been sufficient advise / suggestions, for more than one Contributor, offered for the User to make an informed and educated choice what the next course of action is required.

The suggestions have been put forth on a volunteer basis, in good faith and in the best interests of the computer.

Why would it actually lie about an adware?

I already explained that. The makers of Avast want you to believe it is actually doing something. It can’t actually do anything it purports to do, so they have to make up things to warn you about to make you think it is useful.

I tried Malwarebytes but it didn't detect ****

Because it is not a threat.

The Only thing this Antivirus software is protecting is the Bank Account of the Developers and for zero return to the User aside from the problems this software creates.