Hi Jean-Luc, CFB and others interested;
I'm ready with that client side implementation of an SHA256 test. I would like some people to test this. I have tested it on the latest Safari, Firefox, and chrome.
As far as I know this will only run in IE10+, earlier versions of IE are not supported.
You can download the files here:
http://nxtra.org/update/update.zipUnzip, then go to your nxt folder and navigate to webapps > root. Paste the two files there.
Now you should be able to open
http://localhost:7874/update.html in the browser.
For this test you will always receive the update notice. An older version is hardcoded in. This is to allow for testing of the sha256 hashing function.
Just follow the instructions; download the client, and then drop it over the dropzone to see if it compares to the official release.
If all goes well you should see this screen:

Now also test it with another file, just a simple txt file or another zip, it doesn't matter. Just pretend this is a fake release.
If that goes well, you should see the following:

I hope this will increase the security of everyone, if you have any feedback, please share.
My Nxt ID for donations is: 3209075099254042753 - any donation is appreciated.
Thank you,
Wesley