For example, researchers designed one system that classified interactive and noninteractive processes automatically by looking at the amount of terminal I/O.
If a process did not input or output to the terminal in a 1-second interval, the process was classified as noninteractive and was moved to a lower-priority queue.
In response to this policy, one programmer modified his programs to write an arbitrary character to the terminal at regular intervals of less than 1 second.
The system gave his programs a high priority, even though the terminal output was completely meaningless.