The attacker really did useful work for 2 years, before taking over the project and injecting malware? I wasn't clear on the timeline. That is pretty hard to

The attacker really did useful work for 2 years, before taking over the project and injecting malware? I wasn't clear on the timeline. That is pretty hard to defend against. I wonder if they were planning this all along, or if they wound up with a greedy plan later, or what.