more info here: https://meltdownattack.com
It seems there is a deep flaw in Intel 64 bit CPUs that may let malware access kernel memory – a bad thing. The OS work arounds for this will cut performance significantly. Technical details are in the linked article.
Windows and Linux are to issue update shortly. Apple’s macOS (nee OS X) has been patched since version 10.3.2
So, if you are contemplating a computer purchase I think you should delay buying until Intel fixes the CPU defect and announces which CPU lines are fixed. Then make sure a fixed chip is in the computer you want.