It appears that Hank
may have become infected with a virus that originated from his computer. If so, this would represent the first instance of a computer virus capable of acting on a biological host. It has been speculated [mostly by me in an IM] that this could be the result of a biological weapons test. Hank seems to be at a complete loss to explain this virus' origins.
Given the amount of time Hank spends connected to the internet, he is clearly at higher risk than most for such infections, so despite the normal precautions to ensure the computer system doesn't get "infected", apparently no such precautions were in place to protect Hank, himself.