Fun. Here's my interpretation of what a scrolling hacker toy would look like... It's 90 characters.

You could make it run for >2.5 minutes by ...

Update: Here is another one that fills in the fixed positions not left-to-right, but randomly, to look more Matrix-like. As it gets more and more characters fixed, it slows down to increase the drama (this is me trying to sell a design inefficiency as a feature). It's 124 characters.

On my machine, it looks nice doing 20-digit combinations.