In Halo 3 ODST, what do the achievements; Good Samaritan & Naughty Naughty mean.?

[Josh]

Im not sure what to do to get them, please help. In the guide it says, 'killing things that are new and different are bad'. I have no idea what this means.

 

[mr_j526]

To get the Good Samaritan achievement, you have to complete the entire campaign without killing any Engineers (the floating guys that create an over-shield on Covenant around them) (only counts the ones that you find at night while playing as the Rookie) (unsure about the self destructing Engineers, some people say that it ruins the Good Samaritan achievement while others say it doesn't; my thought is that if you see an engineer with Covenant forces, avoid them and either get past them or find another path).

Naughty Naughty is the opposite, you have to wander around the city as the Rookie and find 10 engineers. Kill them and you will get the achievement.