Device: MacBook Pro 9,1 (15-inch unibody mid-2012), 750GB HDD, partitioned to 600GB OS X, 150GB Windows. The past two days have pretty much been my technological nightmare, that I have been wondering about for years... Would something like this ever happen to me? The answer is yes. I am writing this both for help, as well as a reference point for anyone else who might come across this. I innocently enough decided to upgrade from Windows 8 to Windows 10. In order to do this, I first upgraded to Windows 8.1, which took long enough, and took the next step to Windows 10. Great! All done, after a massive struggle (I remember why I prefer OS X..) During the installation process, because my default startup hard drive was set as Macintosh HD, I several times killed the boot process by holding the power button due to Windows wanting to restart. After waking up the day after starting the Windows 10 install process, I came to my laptop which had hung about halfway through the startup process. I thought nothing of it, killed it again, and tried to boot up. Nothing! It shut itself down at the halfway mark. I took my MacBook Pro with me to university and troubleshooted using: Diagnostics (holding down D during startup, came up with nothing) Recovery, pretty much useless. Tried to repair the disk three or four times. Each time, it let me know that the drive could not be repaired and I should format it. Single user mode and ran fsck many times, came up with incorrect number of thread records (4, 23745) every time. Now funnily enough! The Windows 10 partition was 100% fine, it even mounted and allowed me to access my Macintosh HD! Which leads me to believe that there is something funky going on with either Windows or OS X. The hard drive itself was clearly physically intact and operating normally. I took it to my local Apple store, where they tried some diagnostics but quickly realised that the hype was real. They kindly replaced my hard drive and hard drive cable for no charge. Wonderful, everything is dandy, fsck Windows 10. Right? Except.. I've just come home and plugged in my external WD hard drive that I used to back up the 500GB of data I had on my previous drive, and this one is exhibiting the exact same symptoms. Won't repair, won't mount, won't unmount, won't eject, won't allow fsck to be run because it's 'busy'. By some miracle as I was typing this, the volume finally mounted. I hit Verify Disk in Disk Utility and it let me know that "The volume corn appears to be OK." Psh. But it certainly has scared me to bits and I'm moving everything important off, and formatting the drive as soon as possible. So what happened here? Did Windows screw up my drives? Or was it completely coincidental? Do I have some corrupt files, or am I the lucky winner of a 'firmworm' infection that everyone is going crazy about in the news? Let me know your theories. Footnote, I did try mounting my external drive on a different mac, and it also came up the same way, unresponsive, Repair Disk came back with 'Cannot repair', etc. The external drive is exFAT. The Macintosh HD was HFS+. Let me know your thoughts.