We had a nice case in my most recent game. An exhuman infomorph had infiltrated the mesh inserts of a PC. It had reached hidden status and quietly replaced his muse - not too easy to notice, since his muse was a former piece of spam that mostly did cryptic things. A few hours later the informorph had quietly copied itself into local blueprints, the controls of the expedition CM and a lot of other places. It had built railgun equipped bots, secretly taken two resting PCs hostage, and was now busy turning the base camp into its fortress. When the PCs found out sparks really began to fly - the infected PC had all his implants shut off from his control, the tacnet became a viral swamp, and all the local defenses turned on the team. Had it been a bit less badass team things would have gone very badly... now they just lost the two hostages, burned the basecamp to cinders, and then spent almost a day obsessively cleaning their software. Ah, the wonders of trauma-induced OCD... In this case I assumed that the initial intruder had digged himself in so deep that nothing but a hardware reset could dislodge him (doing a hardware reset on your implants while in a spacesuit is also a bit challenging). Worse, it had left code in a lot of the equipment to allow it to bounce back. The later forks had not had time to be so through in their hacking, so they could be ousted with sufficiently good InfoSec rolls - and they were of course doing counter-attacks.