When I have a chance, I intend to read more thoroughly this paper, which I've only skimmed so far: "Would contact with extraterrestrials benefit or harm humanity? A scenario analysis." (I wrote on a similar theme a few years ago.)
The paper has caused a bit of kerfuffle, involving sensationalism, misunderstanding and politicization. See:
"Some important points of clarification," by one of the paper's coauthors.
"Bad news from NASA: If we don’t reduce carbon emissions, the aliens might come and kill us; Update: Not a NASA report," Hot Air.
"Right Wing Blogs in Massive Anti-Science Fail Mode," Little Green Footballs.
UPDATE: "Space Aliens Are Probably Progressive Liberals," National Review.