You are very right. A zero day and rootkits are NOT known in the wild yet. However, this has been going on for months upon months. The reality about rootkits (especially firmware rootlets) is that they are virtually impossible to detect unless you are a highly trained professional or data forensics specialist. Rootkits are essentially impossible for even your above average techies to find. This makes "Known" infections, a myth, as discovering a rootkit without being an engineer is a fools errand. Its the equivalent of chasing a ghost. So obviously, there aren't going to be "Known" infections of rootkits. But chances are, they are out there, and you could even have one without having a clue. As in the case for me, (after countless days and nights utilizing the process of elimination) I am fairly convinced that my 3 potentially infected macs (and router at this point) have either traveling root kits, some very very odd incompatibility with El Capitan and Trim on an older hard drive + externals, or just some other insanely unique hardware problem in my 27" 2009 iMac, as well as my 2010 MBPro. I really can't figure much else out. After some reading, it seems as though "TRIM" settings on certain hard drives by different manufacturers can cause symptoms similar to this. However, I don't see why this problem would arise so randomly.
I've logged over 127 clean installs and have found the problem (as well as many other added quirks and erratic behaviors including a reappearing/dissapearing wifi card that sometimes is recognized yet fully functional according to hardware test) to reappear every time. Disk Utility and disk warrior (both legal versions, none of this downloaded stuff), both tell me that my hard drive is okay. As for I/O Errors, I am not sure, as I don't know how to check for that. I'm assuming it would be somewhere in the logs? However, I NOT getting any kernel panics. Files are duplicating themselves, deleting themselves, etc. iTunes tends to go haywire and completely duplicate libraries or half libraries, and then scatter music all over the place as well. Files from before my clean install start appearing on my desktop after my clean install when they were clearly deleted from a clean install.
UPDATE: I finally took my iMac 27" into apple for the millionth time at the 4th store and told them I wasn't leaving until they diagnosed a specific problem and fixed it. I insisted that they trust ME over their POS (not talking about point of sale here) apple diagnostics tests. They took the computer in and called me a day later saying once again "It passed our hardware tests so we did a clean install and everything is working fine". My immediate response was "DID YOU TEST THE WIFI CARD?" to which they said, YES. And affirmed again that it passed diagnostics. Okay, well weren't they in for a treat when I arrived to pick it up beat red in anger, and told them that I wasn't gonna take it back until they plugged it in infront of me and proved to me that the wifi card works and doesn't cause the mac to power off. Well well. They did just that, and Finally I got my small taste of satisfaction as the apple genius immediately became an eye witness to a computer crashing after a few seconds of running the wifi card. On top of that, he got to witness yet another frozen hard drive on the desktop, and hauntingly flashing screen changing backgrounds and desktops as if my mac was just part of a virtual environment to someone else's computer. I finally jumped at the opportunity to tell the apple genius "your Diagnostics doesn't detect a **** thing, and this is what I have been trying to tell you the last 7 times i've been here". Finally, they took it back without me taking it back home thank god, and told me they would replace the wifi card. They did just that and a few days later, my mac seemed to be okay. Ahh... wait a week... Yep, everything is back to complete normal disfunction. But the wifi still works at least. However, the ghost in my mac has not vanished. I don't have any other clue what to do unless there is someone in here who knows something about trim settings and compatibility with non-apple hard drives and if trim could self-activate and transfer itself to other drives as well, or if someone knows how to test my firmware for a rooted bios (which is seemingly impossible). That would be great! Anyway, let me know. This thing gets worse and worse. Data scattered, passwords changed, accounts taken over. Also, does anyone have a clue as to why El Capitan won't allow more than 30 characters for a login password? Seems as though overtime i create a password thats too long, i essentially permanently lock myself out of my mac. Ugh..... Apple, what happened to the days when we were friends and everything just worked like I wanted it to?