Virus Cleaner is a homebrew NES game by Roth. Goal is to sweep away Viri from the playing field, while it’s being protected by some sort of electric waves going around the screen.

To support the growing NES community, Roth released the source code of his game – although it seems not to be very well documented, it might be useful for others. In the case you are not a coder, you may still go to his page and grab the release for a few minutes of gaming fun.

http://robertlbryant.com/index.php/gaming/development/nes-virus-cleaner/