Downloading Software installs McAfee Security Scan without permission

I've personally followed up on several dozen reports like this.  Given sufficient information, I am always happy to follow-up again.

That said, every time I look at this, it consistently comes down to a situation where a third-party browser plug-in (ad-blocker, anti-tracking plugin, etc.) caused the JavaScript on the page to execute in a way that was different than what was actually written (e.g. they blocked the UI with the opt-out), or the software was downloaded through a third-party UI (a browser add-on manager, etc.), which linked directly to the assets that had the optional bundled offers.

In general, the following always works:

• Always get Flash Player directly from Adobe, at https://get.adobe.com/flashplayer/
• If you use browser plug-ins that interfere with the normal operation of the page, you'll want to whitelist them or disable those plug-ins temporarily

Once you have Flash Player installed, you can completely avoid this workflow (and the possibility that any bundles get installed), by doing the following:

• Choose Allow Adobe to Install Updates (recommended)
  Future updates to Flash Player will be installed automatically.  You'll never see a bundled offer unless you need to reinstall.
• Use a browser that includes Flash Player as a built-in component
  In these instances, there's nothing to install, and updates are handled by the browser or operating system
  • IE and Edge on Win8+
    Both include Flash Player as a built-in component, and updates are delivered through Windows Update
    There's nothing separate to download or install
  • Google Chrome on all platforms
    Flash Player is a built-in component of Chrome.  Updates are delivered by Chrome's update mechanism

In the very unlikely event that you encounter a situation where the wrong payload was deployed (i.e. you opted out, but got the bundled offer anyway), I'd be more than happy to investigate.

Adobe uses a global Content Distribution Network (CDN) to deliver content.  Knowing the geography and language in play might help me track down any highly localized problems with a specific CDN node or translated page.

The following information about your environment is also always helpful and appreciated:

https://forums.adobe.com/thread/1195540