you'd be surprised that even intel cpus have it's own 'software' which are called microprograms which runs on 'microcodes' (these are stored in the cpu itself, compared to windows in your hard disk). the errata happens when these microprograms is not handling the operations correctly.

and dont blast me im just giving a very crude example.

so the hotfix is basically a 'microcode update', fixing the problems in the cpu.
i think MS has released microcode updates before for intel cpus.
but usually nothing serious...previously the more serious one was called the FDIV bug, go give it a wiki