A study at Penn State in conjunction with NASA has just been released, outlining the different scenarios that could occur should Earth ever be visited by an alien species. The study, titled "Would contact with extraterrestrials benefit or harm humanity? A scenario analysis" includes the following theory:
Humanity may just now be entering the period in which its rapid civilizational expansion could be detected by an ETI (extraterrestrial intelligence) because our expansion is changing the composition of the Earth's atmosphere, via greenhouse gas emissions. A preemptive strike would be particularly likely in the early phases of our expansion because a civilization may become increasingly difficult to destroy as it continues to expand.
In other words, we're fucking up our planet so much that other species in the universe might take it upon themselves to eliminate us—for the good of the rest of existence. This report has made the rounds (International Business Times wrote at least three articles about it today) but here's the thing: This isn't news. This is the plot of The Day the Earth Stood Still.

Of course it's possible that aliens could destroy us to save the rest of the universe. It's also just as possible they're as equally fucked up as we are, and could come to us for help. Or perhaps they will come to enslave us or have sex with us, or have sex with any of the other species on our planet (duh!), or perhaps just come down and steal our minidonks (again, for sexing) and leave the rest of us alone. Instead of reading this study, you'll probably learn just as much factual information about alien culture as you would scrolling through Blogtown today.

The study also suggests that we shouldn't broadcast any information into space that could be used against us, including our biological makeup. Whoops. I guess it's too late to get back the Voyager Golden Record—now our enemies will be able to defeat us with knowledge of Chuck Berry and how to say hello in Hungarian. Nice going, Carl Sagan.