Humorous SF aside, the worst that will likely happen with the messages is that they will be totally incomprehensible to the recipients, other than their being of deliberate intelligent origin.

I would like to think that the ones gathering all the messages to be sent out wil have some kind of plan to make them understandable at some level, but I have my doubts. The lack of real data on the Web site doesn't help.

Apparently once again they just assume that people will think if their messages get beamed into space by a big antenna that alien beings will pick them up, translate it with ease, and respond in kind.

Of course we have no idea if there are any beings at any level in the 47 UM system. This is more a celebratory stunt than anything else. The best we can hope for is that someone will detect the messages some day and recognize their intelligent origin. And no, I don't think it will make some malevolent ETI aware of Earth and come to invade.