"When Spectre and Meltdown hit just after New Years, it kicked off a flurry of responses from companies like Intel, AMD, ARM, and Microsoft. Patching the flaws, which exploit flaws in branch prediction and speculative execution, has taken several months, with some high-profile failures: Intel had to yank Spectre patches for certain older systems after it became clear they were causing frequent reboots. Fixes resumed rolling out some weeks later, with plans to patch chips as far back as 2007. Those plans have now been canceled.
Previously, we expected Intel would patch Bloomfield (45nm, Core i7), Clarksfield (45nm mobile Core i7), Jasper Forest (45nm Xeon), Penryn (45nm mobile Core 2 Duo), Yorkfield (45nm Core 2 Quad), and Wolfdale (45nm desktop Core 2 Duo). Intel’s SoFIA line of processors, some of which are still sold today, was also set to be updated as well. None of those updates, however, are going to happen."
Article: Intel Won't Patch Older CPUs to Resolve Spectre Flaws - ExtremeTech