How do I get rid of "weknow.ac"?
It sounds like the Flash update you installed was fake, I would suggest you immediately stop using secure sites like online shopping and banking.

Personally I am probably a bit paranoid, so I would be worried about any other stuff that has been installed and would be looking to do a Anti Virus scan and backing up all my data and reinstalling the operating system.

However looking online it appears that these fake Flash installers typically just install a few browser extensions and a security profile.

The extensions you seem to have handled, but the security profile requires a little more work....


Go to System Preferences.
Click Profiles.
The list will include an item "AdminPrefs".
Select this and click the remove - button in the lower left corner.


This will remove the security profile, you should then check all browsers, Chrome, Firefox, Safari, and Opera (if you have these installed) and remove the extension/verify it is removed.

Then finally finish up by resetting the browser settings for these browsers, to avoid repeating this information I'll reference this article for that:
https://www.bugsfighter.com/remove-weknow-ac-mac/

Again I would be mindful that while this is how you are able to remove this malware, I would personally be concerned and would be looking to backup and reinstall my operating system.