Ask HN: Is it safe to use Alexa Echo?

After setting up Alexa Echo, it starts to listen to what we are talking so that it can wake up and answer our question. However, this raises a concern about security. Since it's listening to us, it means it would listen to everything we talked. What if we have told some secrets such as password, bank account details etc without noticing that Alexa is listening? Will this be a huge loophole that our privacy would be collected by Alexa? How could this issue be resolved?