Summary Box: Google adds games to Plus service

GAME ON: Internet search leader Google Inc. is adding a new twist to its duel with Facebook by adding games to its recently introduced social networking service, Plus.

THE OBJECT: Google is hoping to give the more than 25 million users of Plus another reason to visit more frequently and stay for longer periods. Games have been one of Facebook’s big drawing cards during the past few years as it expanded its audience to more than 750 million users.

THE THIRD PLAYER: Google’s move also could affect Zynga Inc., which makes the most popular games on Facebook.