They may masquerade as codecs or updates, but they’re programs.
You should be extremely careful about the programs you download and run because they can gain full access to your computer.
Even Microsoft’s neglected Windows Media Player can play back .mp4 files, which is now the most common format.
Silverlight is vanishing, too — Netflix just dropped the Silverlight requirement and now uses HTML5 video.
At the moment, you’ll only need Silverlight installed if you want to watch Netflix in Firefox — Firefox is working on adding the required “encrypted media extensions” (DRM) code to the browser so it can work.
This particular scam is easy to understand — if you download and run the software, your computer will be infected with something nasty.
It could be a Trojan or other serious case of malware — or just spyware and adware.