Netflix, the popular online movie rental service, is planning to award $1 million to the first person who can improve the accuracy of movie recommendations based on personal preferences.

James Bennett, left, a Netflix vice president, with the company’s chief executive, Reed Hastings, in a headquarters screening room.

To win the prize, which is to be announced today, a contestant will have to devise a system that is more accurate than the company’s current recommendation system by at least 10 percent. And to improve the quality of research, Netflix is making available to the public 100 million of its customers’ movie ratings, a database the company says is the largest of its kind ever released.

“If we knew how to do it, we’d have already done it,” said Reed Hastings, chief executive of Netflix, based in Los Gatos, Calif.

If no one wins within a year, Netflix will award $50,000 to whoever makes the most progress above a 1 percent improvement, and will award the same amount each year until someone wins the grand prize.