Summer Wars is a sci-fi anime film that came out in 2009 and was directed by Mamoru Hosoda.

Kenji Koiso, a mathematically gifted teenager, is met with a request from Natsuki Shinohara, one of the most popular girls in school, to take a trip to Ueda for a family get together. It is Natsuki's grandmother's 90th birthday.
Summer Wars introduces this idea that there is a large world wide network, Oz, that everyone in the world depends on. Oz can be used for conducting business deals, paying taxes, and even online shopping.
During Kanji's visit, Oz is suddenly hacked by an AI named Love Machine. When Kenji gets blamed for being the controller of Love Machine, the Jinnouchi household suddenly goes crazy. Love Machine is trashing the network of Oz. Oz =has control over water pressure, Traffic signals, GPS, and even emergency calls. Kenji must help defeat Love Machine to get the world back in order.
While Natsuki and Kenji are the main characters, the real person who brings this whole movie together is Natsuki's 90 year old grandmother.
Summer Wars offers startling plot twists and an amazing story of family and perseverance. Summer Wars is a definite must see, and a good buy.