From WikiPedia: "(Asteroid) 1950 DA is the near Earth object with the highest known possible probability of impacting Earth, according to the Palermo Technical Impact Hazard Scale. For a few days in December 2004 it was temporarily surpassed by 99942 Apophis (which at the time was named only by its provisional designation 2004 MN4)."
It is projected that asteroid 1950DA will approach the Earth on March 16, 2880. They predict two possible outcomes. One, the asteroid completely misses the earth by millions of miles. Two, it will have a 1 in 300 chance of hitting the earth and devastating the human race. If you want to know how we plan to protect ourselves, check out the following Wikipedia page.
For more information, watch this video.