This is a security setting on your system that is resulting in this behaviour, not Flash Player installer itself, or anything with the installer. There are many Google search results on this. The first hit I got, was the following from the Microsoft forums:
To unblock a software publisher:
1. In Internet Explorer, click the Tools button, and then click Internet Options.
2. Go to the Content tab, Look under the Certificates section.
3. Click on Publishers button.
4. Select the Untrusted Publishers tab.
5. Select the Publisher you wish to unblock and click the Remove button.
You found the same solution I did.But it's for Internet Explorer and I'm using - "FIREFOX Browser".
How do I unblock a publisher in Firefox ?
Apologies for not responding sooner.
That solution should work for any executable.. The article I linked to is an easy way to get to the Certificates. Another way to get to Certificates listed here, Certificate cleanup for most personal computers, although the purpose of this article is slightly different, it'll take you to the same general area.