An international partnership on cybersecurity can mean many things--it can mean mutual assistance with enforcement and criminal investigations, or sharing threat information and intelligence, or jointly developing software that can be used to target adversaries' computer systems, or even jointly developing tools and techniques that can be used to detect and mitigate threats. An "impenetrable" unit hints most closely at the last of these functions--a defensive joint effort in which the two countries share not just intelligence but also technical expertise and controls to protect their systems against intruders. But people who help design and implement your defenses then know an awful lot about the way your systems work and how, precisely, they are protected. Possibly, they're even writing code and giving it to you to download on your computers to help make them more impenetrable. And if that code also created backdoors on every computer it was installed on so that Russia had easy access to control those systems, who would be surprised?