Issue opening alsmost any file

[RovakX]

Here's my situation:
I'm getting this notification when I try to open any file acquired over the internet.
This image was the first time i encountered the problem, but ever since any file i download, I can't open.
I tried Microsoft office files, PDF, Zip files, some video's, mp3, aac, Jpg, ...
I tried transfer over gmail (via Mail app), facebook, directly from a website.
I tried opening a file with different apps eg word, textedit.
All with the same result.
When I download the same file on another device, then transfer it via USB stick, I managed to open a word document and a jpg.
Any files created on this machine open just fine.
an .avi movie downloaded with torrents do open for some reason (I played it with VLC, opening music files with VLC doesn't work though)
Apps open just fine

The problem started yesterday evening, after transferring this .docx file via email.
Other files, witch I opened yesterday morning, and I can't open anymore.
Another weird thing is that I can view most documents like pictures in finder, (by pressing spacebar when a file is selected) but when i then try to open them, it wont work.
(I also tried turning my firewall off before downloading a file, nothing helps)

Please someone help me!
I have a time machine backup from a few weeks ago, if all else fails.

Macbook Pro 15" Early 2011
OSX Yosemite 10.10.5
2GHz Intel Core i7
16GB 1333MHz DDR3
Mackintosh HD
AMD Radeon HD 6490M 256MB
Safari 9.0.1

Anything else you need to know?

 

[honestone]

Wonder if that file "infected" Safari? Have you tried another browser?

If worse comes to worse, assuming either the Recovery Partition is on your internal drive, or better yet, that you can boot your machine from an external device (that's where a product like SuperDuper! comes in handy), you can use Disk Utility to Erase, Format, and Partition your internal drive. Then, do a clean installation of OS 10.10.5 (either via the "full" OS 10.10.5, or starting with OS 10.10.0, and using the Combo Updater for OS 10.10.5). After that, use Migration Assistant to get your stuff from that Time Machine backup. Finally, download and install Safari V9.0.1 (available from here: http://www.macupdate.com/app/mac/15675/apple-safari).