http://io9.com/5921814/is-seti-at-risk-of-downloading-a-malicious-virus-from-outer-space
.....When we asked Cirkovic what the purpose of an ET virus might be, he responded, "If we discard anthropocentric malice, it seems that the most probable response is that they have evolved autonomously in a network of an advanced civilization -– which may or may not persist to this day." If this is the case, speculated Cirkovic, these extraterrestrial viruses would probably just replicate themselves and subvert our resources to further transmit themselves across the Galaxy. In other words, the virus may or may not be under the control of any extraterrestrial civilization –- it could be an advanced AI that's out of control and replicating itself by taking over the broadcast capabilities of each civilization it touches. A very frightening thought.