Will talking to the two secruity guards in the third mission disqualify me from getting the Ghost experience bonus

This post is a wiki post. Please feel free to edit it, but with first-hand information only.

First-hand testing has established that the Ghost rating is still achievable with:

• A camera becoming "suspicious",
• Turrets seeing you, firing at you and getting destroyed by you, as long as no living enemy seen/heard it,
• A guard getting "alarmed" by seeing/hearing an effect, like a very short (<1 sec) visual PC presence, a door opening, jumping or gunshot,
• Killing or knocking-out enemies with a takedown from behind, if nobody saw you,
• Insta-killing someone (probably with a headshot), as long as they didn't have a chance to see you & react, and nobody seen it,
• Insta-knocking out an enemy with a tranquilizer dart to the head (you'll see the Marksman reward), if nobody sees it - note that not every enemy (particularily those with heavy helmets) can be insta-knocked out.

However, you will not get the rating if:

• Enemy sees player for a bit longer (getting Hostile in the meantime), touches player or sees him carrying something,
• Any enemy sees a bot/turret destruction, ally death or an unconscious/dead body,
• Enemy sees a gunshot (only hearing it is still OK!).

Note that having a "Hostile" enemy doesn't automatically mean you lost "Ghost"; e.g. a lone enemy attacked by reprogrammed turret would get Hostile, but you still can get Ghost in that situation, if all the other conditions are met.

For more reference & test cases, see http://deusex.wikia.com/wiki/Ghost_%28bonus%29

Note that the Smooth Operator reward is an "easier" version of Ghost, which only applies to avoiding triggering installed alarm-systems, not detection or combat with guards themselves. (It cannot be rewarded for passing areas that lack such systems.) Smooth Operator is used for the Foxiest of the Hounds achievement.

1. You can be detected by these people and still get the reward for being sneaky. As long as they don't go Hostile, you're fine.

2. You can make this jump without the leg aug, but you need the Punch Through Walls aug to go this way. This also involves snapping a guy's neck and will ruin a pacifist playthrough. Also throwing a grenade at the wall works, and only knocks the guy unconscious., or you could just use the ventilation ducts attached to the wall...

3. As before, if they don't go Hostile, you are fine.

The game will tell you if you fail the sneaky objective.