A year ago, in January 2018, three hardware vulnerabilities known as Meltdown, Spectre Variant 1, and Spectre Variant 2 were disclosed to the public.
Although disclosure was supposed to occur on January 9, news outlets found updates in the Linux Kernel and broke word early on January 3, kicking off the year with a pretty big headache for IT and security teams across the globe.
These vulnerabilities were described in detail in different papers and articles quite rapidly following the disclosure. A summarized way to describe the vulnerabilities would be that speculative execution, a feature used by CPUs to predict what to do next and improve performance, could be exploited to get programs to reveal information they should not have access to. The full papers are a great read.
During the first weeks, information on what patches to deploy, features to enable, and what vulnerability they actually fixed were updated daily, causing a great deal of confusion.