And this, my friends, is how Mati and Observer's post counts rise so quickly.
No, you haven't just discovered that bug. When you get to about $4 billion, your cash (or company value, in this case) gets so big it can't fit in the variable it's been allocated internally. It 'flips' the sign bit, and $4 billion becomes minus $4 billion! Your cash will soon go the same way. You must quickly spend a lot of money - fund a few industries, or do some advertising campaigns.
And yes, I did know about the title screen. I knew that a couple of years ago.
![Razz :P](./images/smilies/icon_razz.gif)