Originally Posted by JuanBeerOrTwo
Besides being messy, is it bad for the beer? Maybe cause contamination?
Nothing to worry about. Your beer is producing so much CO2 that it will help to keep any infections out of the carboy. It's similar to an open fermenter when the airlock is not place.
As others mentioned, a blow off tube is in order. I use one on almost every brew just to be on the safe side. The blow off tube can either be inserted into the carboy opening directly, or into the airlock with the other end going into a container of sanitizer.