Last night, one of my clients' sites was hacked.
The only thing that's been done by the hackers, as far as I can see, it that they changed the content of the index.php file to theirs.
The fix for that was done very quickly, of course, simply by replacing this file back to the original one I had from the latest backup.
As far as I can tell, they didn't reach the WP admin, as nothing else is missing from the files, and once the main file was restored, everything worked fine.
So how do I find out how they did it?? In order to prevent it from happening again, of course.
I have a paid account at WPMU and the Defender plugin installed as part of this, but it doesn't provide much valuable information and nothing relevant to this case, anyway.