>>> I'm not sure it's that difficult for Microsoft. Yes it is. AV use various hacks and exploits to hijack calls to the kernel. How did you think they notify

>>> I'm not sure it's that difficult for Microsoft. Yes it is. AV use various hacks and exploits to hijack calls to the kernel. How did you think they notify you of an infected file before you open the infected file? The AV intercepts kernel API calls to list and open files. I wouldn't be surprised if the patch for meltdown/spectre breaks these techniques. Generally speaking, these techniques will crash the system if they didn't work as intended. Microsoft doesn't want AV to BSOD millions of computers so they don't update when they detect an AV. It's perfectly reasonable to me.