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? Edit: I found a way to open files, by opening the app first ant then clickinf file > open file > .... So I was thinking maybe a problem with Finder? but then why only downloaded files?