"Virus" has at least one thing - a very descriptive title.
It is a virus you are playing, in all of its beauty, meaning an invisible cloud of particles trying to rot out all of humanity. Well, I made the cloud green so you can see where you are, but except that, there's not much difference.

Having that in mind, your goal is to infect as many humans (the black, simple-shaped things) as quickly as possible. Let your cells grab onto them to live and thrive, grow, and eventually win. Failing to do so would mean your own death, since mankind won't just let you do your thing without trying to create some form of medicine.

Anyway, so much to the story itself. Now to the technical and non-technical aspects.
The game was written in Java using my engine JangoDare (http://github.com/JangoBrick/JangoDare). GIMP for graphics, FL Studio for music (Yes! Music! ... kind of!), Audacity for audio editing.
The whole thing took me about 27 hours, minus ~9 hours of sleep, makes approximately 18 hours.
Didn't spend longer on it because I started over 15 hours in.
Was a lot of fun!

I hope you're having at least half as much fun playing it, then I'd call it a success.
Oh, and if your ears freak out, the music can be turned off ;D