Are asteroids a threat to us?

Yes, they will not be broken down by our atmosphere what i believe the person who answered previously is referring to are comets which often are broken down to a point where the impact is of no threat. But asteriods are indeed a threat, all that could possible be down is track it down in time to try and stop it before it hits. I believe that the most dangerous asteriod are the ones that orginate from the belt after pluto, not exactly sure if thats correct though just going on basic knowledge.