It is now known that Intel (and possibly other CPU manufacturers) have a very serious design flaw with nearly all their CPU’s. Most of the explanations thus far are far too detailed and confusing for even tech’s to understand. We have laid out what you need to know in two sentences per category.
The crux of the issue is that the CPU keeps a table of memory locations and it is possible for malicious code to poke at that table and find out what other software has in memory. This could be things like your password or financial data.
The solution is to separate the operating system Kernel (Windows, OSX, Linux…) memory map from the memory map for programs. This is likely to result in a notable decrease in performance.
WHAT, ME WORRY?
Even though this issue (I would not call it a bug) occurs on with all operating systems, developers like Microsoft and Apple were quietly made aware of the problem (likely in early summer of 2017) and have been working on a fix. Those fixes should be released shortly.
Strangely Intel, Microsoft and Apple have not yet made an official announcements. AMD has said they are not seeing the problem.
This video does an excellent job of explaining the Intel CPU design flaw in more detail without requiring a PHD to understand this very complex engineering problem.
If you want more detail, there are several sites including the venerable ARSTechnica that provide a full write up on what this flaw is about and how it is being addressed.