Randy Pitchford, via Twitter, has Tweeted out a couple of images and messages saying that a bomb disposal unit has just arrived at the Gearbox parking lot. According to Pitchford, they are there in response to the threat of a car bomb at Gearbox HQ.
Someone is out of control! Bomb disposal unit called to Gearbox HQ parking lot to deal with car bomb threat. (#1)

Bomb disposal robot in action in Gearbox HQ parking lot! #friday (#2)

Details are scarce but it seems as though the bomb disposal team is still on sight and looking for anything suspicious. At present, there is no word on what prompted this action or who may be responsible.

UPDATE: Randy Pitchford has provided a few additional Tweets to let everyone know that everything and everyone is ok.