Depends how resilient they can make it, and how much they need. There are plenty of espionage stories involving being stuck by needles without knowing it. Or if

Depends how resilient they can make it, and how much they need. There are plenty of espionage stories involving being stuck by needles without knowing it. Or if they can get it into your food (but they'd have to make it resistant to being digested). Or if they can aerosolize it and spray it on you. The truly scary thing is if they can make it contagious, but only effect the target. There are so many benign strains of DNA that we just live with it would be hard to detect. Then you just infect someone close to the target and wait for them to be effected (and perhaps some collateral damage from those unlucky enough to be similar enough to the target). The nightmare scenario is not when terrorists use this to target specific groups of people (e.g. all women, all people of a specific ethnicity), it's when it goes beyond our control by accident and contaminates all of our bodily fluids.