I disagree. I don't think the DHARMA computer device was rewired by the hostiles or anything, and I think the C4 was set their by Dharma as well. Think about it, if they knew the Hostiles were this big threat, the last thing they want to happen is that this (possibly) ONLY way of communicating with the outside world is to fall into their hands.

It reminds me of Stargate SG1, whenever Stargate Command is compromised, the person in charge will immediately start a self destruct countdown to destroy the base to stop it falling into enemy hands.

DHARMA knew that the hostiles might try and take the facility, they also knew it was extremely important (possibly the only communcation with the outside world) so they set C4 to destroy it should it fall into enemy hands. "Has the station been taken over by Hostiles?" If yes then "BOOM". There was even a timer long enough to allow escape from the building. Makes perfect sense.