Hi. Encountered a horrible issue on my 27-inch iMac (mid-2011) just before Christmas and was wondering if anyone else had encounter the same problem. I had been surfing my regular websites in Safari when the screen went white, and after a few seconds the iMac restarted. Once restarted, after logging back into the iMac, the same thing happened before I could do anything else. Fortunately I have MacBook which saw me over Christmas, but having tried various options such as starting in Safe Boot first (which was OK), and using another account I have on the iMac (which was OK), logging back into my normal account and launching Safari resulted in the same white screen/restart. So I used safe boot again, sent all the Safari caches and preferences to the Trash, and did a hard boot. This seems to have cured it, but I would be very interested to know if anyone knows what may have caused this. I am assuming that a website has cached something that OS X doesn't get one with, so would like to avoid that website if possible. I am on OS 10.11.2 and Safari 9.0.2. Any ideas/assistance gratefully received.