This doesn't appear to me to have anything to do with using Outlook as a mail client
Not necessarily Outlook, but any program that uses IE to render HTML and has auto-preview features. But you are right, Outlook has it's own security problems (well, MS calls them features) and I don't think this is directly caused by one of them this time.
It does, however, seem to have a lot to do with a third party download server not keeping up their housekeeping.
They do not guarantee virus free files, so you can't really blame them. Sure it's nice of them to run a virus scanner on their servers, but it's not their duty. Downloading a file from any 3rd party you take a chance.