By using a "crowdsourcing" application similar to the ones used by SETI and Galaxy Zoo, scientists are proposing a search for evidence that extraterrestrials once visited the moon. No, they're not proposing ET has visited. Rather, since we have a space probe up there sensitive enough to spot Apollo astronaut footprints, if there are any footprints made by anybody or anything else, we'd be able to see them. They're just proposing someone start to look.