Everyone is now talking about the CPU security problems that are now being fully disclosed: they’re dubbed Meltdown and Spectre. Meltdown is a problem that mainly or entirely affects Intel CPUs, but Spectre is a problem that affects all designs.
I haven’t seen any “explain it like I’m 5” on the Spectre paper yet, so here’s my take. Sadly, it’s not 5-year-old level, but I’ve tried to make it a bit more accessible. If you want a lot more detail, the Google blog has code.