Well the comment that was give by Tom when he catches Locke, Sawyer and Jack he tells them not to cross this side of the island he says some slick line like "You all come into our neighborhood, eat our food and open "doors" you shouldn't be opening"

The only door the Losties opened was the Hatch so the statement above indicates they know about it. However, your right in the sence they may not know what it does. However, we know the computer could have done more then just type the numbers because Michael used it when he thought he was communicating with Walt. And no one builds a full blown keyboard when they can only use it for some numbers and an execute button. So that must mean that computer could have done more then just what the oreintation said it could do.

Also, In the map on the blast door it form Lostpedia it reads in the lower right activity minimal during lockdown and restocking procedures. After the lockdown happened, a pallet of food was found in the jungle near the hatch. Charlie makes some connection between the two by saying something like “maybe that’s why the doors went down so no one can see where the balloon was coming from”

Either way I think Ben knows what the hatch is about and planted an evil seed inside Locke’s mind in order to question its purpose. Ben must have known it would have knocked down their communications. So he lied to Locke and led him to believe nothing would happen. After all he clearly has no intentions on leaving the island nor does he want any one else to either. He made it very clear he couldn’t just do whatever he wanted because the “others” would question his motives and trust.

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