Use of the requested audio unit(s) require lowering the security settings

I just started getting this alert at seemingly random points in Finder:

Use of the requested audio unit(s) require lowering of the security settings for "Quick Look UI Helper". Are you sure you want to proceed?

[Lower Security Settings] [Cancel]

This appears even when the selected item in the Finder cannot be quick-looked (e.g. AVI files).

Does anyone have any idea what it means and what causes it? This hasn't appeared before the latest software update and no search results match the alert text, so I'm suspecting this is something new in the OS update.

OS: macOS Sierra 10.12.4
Hardware: Mid-2012 MacBook Pro

I have come across one (!) reply on the Apple boards.

I want anyone who reads this to take it with a grain of caution. This 'answer' does not seem to ring as '110%' accurate.

You are using a Codec component that is not compatible with macOS Sierra. That Codec component was a part of a library that conflicts with macOS Sierra and in order for Quicktime to load would require to change the "Quick Look UI Helper" security settings. If you really need that Codec component you can proceed by clicking "Quick Look UI Helper" Lower Security Settings.

(Here's the link; https://discussions.apple.com/thread/7948198?start=0&tstart=0)

Just came across this issue for the first time and have an answer for how to fix it (without blindly lowering your security settings.)

The good thing about TimeMachine is that you can transparently transfer files when you move computers. This is also a bad thing. The software causing this issue for me was a codec pack I installed in 2006(!) and had long forgotten about. Take a look through the following folders, looking for anything that you don't think you need (if you installed it 15 years ago, you probably don't need it!)

~/Library/QuickTime/
~/Library/Audio/Plug-Ins/
~/Library/Audio/Plug-Ins/Components/
~/Library/Components/

After deleting items (e.g. rm -rf ~/Library/Quicktime/Perian.component in my case) restart Finder (sudo pkill Finder in the terminal) and try using Quick Look again.