https://arstechnica.com/gadgets/2018/02/intel-releases-new-spectre-microcode-update-for-skylake-other-chips-remain-in-beta/

After recommending customers not use its microcode fix for Broadwell and Haswell chips, Intel has issued a new microcode update for Skylake processors that gives operating systems the ability to protect against the Spectre flaw revealed earlier this year.

The Spectre attacks work by persuading the processor's branch predictor into making a specific bad prediction. This bad prediction can then be used to infer the value of data stored in memory, in turn giving an attacker information that they shouldn't otherwise have. The microcode update is designed to give operating systems greater control over the branch predictor, enabling them to prevent one process from influencing the predictions made in another process.