We all know how internet advertising works but things were a little different back in the day. The OP remembers how there was a company called AllAdvantage that would pay you to download their banner and get exposed to their ads. The longer you were online, the more money you could make.
However, the clock would stop if your screensaver came on or if your computer went to sleep. The OP figured out that all they needed was a program that would slowly move the mouse while you were not even actually there to keep the AA clock ticking. Evil genius!