Let's Pretend: If It's Not a Virus, What Else Could It Be?

[Osiris]

I think it's code. Been working on cracking it all day, but the key escapes me. I've tried Dr. Seuss, but I'm coming up empty.

Back on track though, I was considering the idea that it was perhaps a meteorite, which could be explained away with the explosion in the beginning of the first episode... but no... the timeline wouldn't match up between Mike hearing the explosion and seeing the news report of the first attacks. Nevermind, it doesn't make sense.