Go have a google, not sure if I remember the exact reason correctly or not, but from my faded old memory, it has to do with magnetic fields. While the magnetic field is active, corrosion can't form, similar to metal boats, and why they use electric current to stop erosion.

Since people seem to be obsessed with my answer and the example I gave and concentrating on the electrolysis portion, I feel it needed more clarification for those obsessed with the example. I first learned about this preventative because I live on an island, and preventing corrosion in electronic equipment is important here.. Electrolysis, as I mentioned with the boat example, creates a flow of electrons, which in turn creates a magnetic field, a magnetic field can prevent corrosion. Electrolysis is not used in a computer because it has a source of electrical current present already and thus a flow of electrons if kept powered.A magnetic field can both prevent and accelerate corrosion depending on the specific metal, the magnetic field's orientation, and the environment, though some research suggests that magnetic fields can reduce corrosion rates in certain conditions by affecting the development of protective passive layers or the behavior of ions. For instance, a parallel magnetic field has been shown to inhibit the corrosion of magnetic materials like carbon steel, whereas a perpendicular field can promote it. The underlying mechanisms, such as magnetic gradient forces and induced currents, are complex and still being studied. Hopefully, this helps clarify my answer that I gave for everyone interested.