Mercifully, some PC invaders are purely terrestrial in origin, although that doesn't make them any less destructive. Ben Wilshaw whipped open a monitor case to find this...
...which on closer inspection turned out to be roasted ants:
There are no ants inside Jim McNelis's machine, because the cockroaches ate them:
I started out thinking "I've seen worse than that", and finished with "holy crap".
What I've learned
It seems that ants are negatively charged - they're all stuck to the positive pin on that capacitor.
And I thought Pratchett made this stuff up!!!