Ask HN: I'm looking for a story (fictional)

I remember reading it on here some time ago. It was essentially about a team of developers that discovered a string appearing in their binaries and tracked it from their project into their compiler. They then tried bootstrapping their own compiler only to find the strings appearing there as well. At some point they begin to suspect that something is sending network traffic that isn't appearing in normal tools and finally attach an old switch to see that packets are being hidden and sent. Finally they receive a letter that essentially tells them that they did a good job finding the bug and that it'll now be retreating deeper into the computer.