system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do companies discover that they've been hacked?

If you're a smart hacker, couldn't you figure out how to access information without anyone knowing that you did it?
gpt
If a good hacker didn't leave a footprint then the company wouldn't know about the leak, and you would never hear about the company having a leak.

The Sony hack wasn't noticed by Sony.  It was the hacker group that publicly exposed the hack.