Days ago, Microsoft rolled out a set of Windows 10 security updates that offer mitigation for Spectre Variant 2. These patches contain microcode updates for Intel processors of the Haswell, Broadwell, and Skylake generations.
The best way to get the microcode updates is via firmware patches from motherboard or system vendors, but an OS-level patch is the next-best way. While hardware makers issued lots of patches for Kaby Lake and Coffee Lake systems, older generations of Intel products didn't see as much love. As The Tech Report points out, this will be the first Spectre Variant 2 fix for many Haswell-based PC owners:
Major hardware vendors have released firmware patches for many or most Kaby Lake and Coffee Lake motherboards and systems. Coverage of Skylake systems appears to have generally been good, but updates for Broadwell systems have been less common. Today's patch marks the first time that many owners of Haswell systems running Windows have received any kind of fix for the Spectre Variant 2 vulnerability.
The update is delivered via Windows Update so there's no need to download it manually.