[Duo laughs dryly.] I only wish. [He flexes his hand a little reflexively, eyes drawn to the nanite tattoo on his wrist. He had no idea if the nanomachines this place had injected into him had interacted with or overwritten the PPP, but he didn't really want to find out.] The "Perfect Peace Program". A medical nanomachine that remains dormant until triggered, upon which time it causes immediate heart failure in its host.

The trigger is... [He casts another sidelong, wary glance] attempting to harm a particular, programmed target.

...When Mars started to attract more workers and their families, complications arose with illnesses. Sorta like the early days of Lagrange colonization. Weird viruses caused by the environment and the bacteria that had populated during terraformation. In order to combat the spread, government-approved vaccines became a requirement of Martian immigration.