Hardware

I ran into an issue where every .exe file I downloaded was detected as a Virus. THe issue was actually two versions of AVG installed. If you don't have AVG then this might not apply to you.

First, check in your browser some have a spot where you specify an AV that could be pointed at the wrong location resulting in false positives.

1. Remove AVG (use the AVG Removal Tool if you can't get rid of it.

2. Go to C:\Program Files (or x86) and delete the AVG folder

3. Reinstall AVG and it'll work

Hope it helps!

The Apple download pages default to providing for the OS you're using rather than a single page saying "hey download any version from here"

you can try downloading on a different computer and place on a usb stick.  Sounds like UAC, defender or AV blocking it from download.  check your windows logs and it should tell what is stopping this.

  While I have no love for iTunes, unless you are downloading it from somewhere other than Apple it shouldn't be inherently marked as dangerous.

  I would definitely check UAC, Windows Defender, and your antivirus as SMal.tmcc mentions, but that message wording sounds suspiciously like it is likely being blocked by your browser security settings for downloads.  For example, in IE9, you can change most of these in the Security tab of Internet Options.