Cean it, and put a fresh airlock on asap. the airlock is not sterile anymore and if you have any blow back you could pull nasties into your brew. My microbiology class did that (and let if ferment in a LIGHT HOT ROOM, not a cool dark basement), I am not going to try their beer because I know it will taste like a skunk's satchel.
wow i'd love to be in that class....i mean aside from the bad beer...any class that will incorporate brewing into any theories being discussed as part of the class, has to be a good class.