Burnt Out Processor Question

Hi, I recently found the issue with one of my PCs to be the processor faulting. I was hoping someone could give me some insight to what may have possibly happened to it.

2500k 1.360v at 4.5hz stable with a temperature ranging on average 20c(idle)-52c(stress test).

It's lasted about a year now, but it's strange, temperature, voltage, heat all seemed within acceptable ranges.
Everything else component wise works fine, but the odd thing is the back of the processor is tainted a very light gray coating over 90% of the back as you can see in the images below?

So any idea on how this was possible? Surge in electricity? Bad processor? Pushed it to far?

May be a bit hard to see, indirect light you can't see it well.