I remember a
Babylon 5 episode, "
A Day In The Strife," where a probe arrives, and presents the station with a test. If they pass, it promises to share advanced technology. If they fail, the station will be destroyed in a few hours. Well, Babylon 5 succeeded in answering the questions. But before the answers were sent,
John Sheridan had second thoughts. He surmised that the probe would likely not destroy a less advanced race, but one that may be able to challenge it. He withheld the answers past the deadline and the probe began to depart. To keep the probe from harming any other race it came across, the answers were transmitted from a securbot far away from the station. This caused the probe to detonate, with an explosive yield of roughly 500,000 megatons.
Moral: Contact from ET may not necessarily be benign.