Unwanted Installation

Can anyone tell me how Avast AV was installed on my PC without my permission. Only I have access to it so it was not someone else. It just appeared as an icon on my desktop and I found it to be installed following a windows update?

I have now uninstalled it but I am very annoyed at how this was done, this is how viruses and malware behave not reputable av companies

Do you have CCleaner? >> https://support.piriform.com/hc/en-us/articles/360001205071-Why-has-Avast-been-installed-to-my-machine-