It's an interesting premise, and was unveiled by Sung Wook Paek, an MIT graduate student, on Friday. The idea won the 2012 Move an Asteroid Technical Paper Competition, sponsored by the United Nations' Space Generation Advisory Council.
Paek's idea is that a spacecraft would fire two rounds (one each for front and back) of pellets full of white paint powder at an asteroid, covering as much of the surface as possible. While the impact from the pellet would already push the asteroid slightly off course, the coat of paint job splattered onto the surface by the pellets would at least double the its sunlight reflectivity.
Increased solar radiation pressure would then push the asteroid further off course. Because of the size of potential threats to Earth and the minute pressure of photons, the mission would need to be performed years or decades in advance.
Paek used the asteroid Apophis as his "test subject" in the paper. was used as a theoretical test case in Paek's proposal. Aprophis is already a subject of some concern among the public, as the 1,150-foot-wide asteroid is expected to come near to Earth in 2029, but then return in 2036. Although both are near in astronomical terms, neither is expected to result in an actual impact.
Paek calculated that five tons of paint could cover Apophis, and that it would take up to 20 years for enough solar radiation pressure to successfully push it off an Earth-bound trajectory. Obviously, Paek's solution requires discovering these threats decades early, not in the timeframes posited in either of the aforementioned movies.
Paek's work builds on 2011's winning proposal, which theorized deflecting an asteroid with a cloud of solid pellets. Solar radiation pressure is already being used in actual scientific experiments: NASA's Messenger spacecraft, for example, uses solar sails to control its trajectory around Mercury.
However, as noted something like this would take years or decades to affect the asteroid properly. Admittedly, the budget for watching the skies for such threats, and finding them in enough time is likely going to be impossible.
In fact, one of the suggestions in the movie "Armageddon" was a set of solar sails. However, due to the fact there were only 18 days left, the suggestion was ridiculed and discounted.