How does Warden/Injection work?

In the recent Ban wave I have heard a lot of people saying their accounts which they never B**ted on/only used CR on were banned. I was lucky enough to avoid the wave, but it got me thinking... I know the only safe way is to not use it at all, but my main question is about multiboxing and injection. I frequently played my main account while the other account ran HB in the background. Would anyone know how "safe" this is HB is only attached to my "spare" account while I do this, and has no injection into the process running my main account.