Can a virus melt the CPU?

"It's definitely possible if the chip failsafe can be overriden. See for example the research paper ""Potential thermal security risks"". From page 4:

Permanent Damage – Disabling the Failsafe. The Intel
failsafe cannot be disabled as far as we know, but older
motherboards for AMD AthlonXP processors did not provide
an adequate failsafe. [13] Although that problem was quickly
rectified, even newer motherboards may allow the failsafe to
be bypassed by disabling the thermal-emergency shutdown
procedure in the BIOS. Obviously, we did not try this, but the
same scenario that engaged the failsafe with the Pentium 4
would overheat and quickly destroy the processor. This is not
reported to criticize AMD systems, but simply to show the
importance of a failsafe mechanism that is hardwired. AMD
has built a thermal trip mechanism in its latest generation of
processors: the Athlon64. Similar to the P4, once the failsafe
is engaged the CPU will shutdown its internal clock and
inform the motherboard to reset through a THERMTRIP pin
[14].

Accelerated aging caused by overheating (also discussed in that paper) is another, less spectacular but perhaps more likely attack.

A third possibility is an attack overclocking a CPU beyond recommended tolerances. For example, although an artificial overclocking lock may be present, it may not be secure, as in the case of the Intel 925X chip.

Note that similar attacks are possible on other pieces of hardware (see the question Can some software physically damage hardware? for details)."

The answer is intrinsically hardware dependent. See Halt and Catch Fire and Killer Poke for some rather out of date hardware that could be damaged by software. Generally such features are regaurded as bugs, and most designs seek to prevent them.

"I believe there are methods in which a virus can modify the cpu voltage. I mean there certainly are HDD-wipe viruses out there.

Anything manipulable can be manipulated.

I'd think a virus creator somehow has to read each motherboards unique ""ID"" or somewhat. Enabling the virus to access the mobo.

I mean there are software out there where you can manipulate your cpu/gpu voltage on-the-fly while the PC system is running in an OS environment. Taking this into account, yes, I believe it is doable somehow.

That being said, nowadays such virus would be moot, since almost any modern cpu has an internal sensor which enables it to shut down once it reaches critical temperatures."

"Maybe!

But it really isn't a relevant concern yet."

"Back in the mid nineties I remember hearing of a, for lack of better word, rootkit that would gain control of the hardware, spike the voltage then open and close all of the logical contacts at once.

Never saw it in action so I don't know if it was vaporware or not."