Mattie (Kristen Bell) goes to visit her friend Douglas Ziegler (Kel O'Neill), a computer geek who has been unconnected for a week. Douglas lets her in into her apartment, but he acts weird and commits suicide in front of her.
Later, Mattie will discvoer that he had been developing a powerful wireless signal and accidentally releases a mysterious force that takes the will to live of the human beings, generating a suicide epidemic which increases the force with every suicide.
When checking his computer, they see many virus appearing on screen and then a virus-page telling them "Do you want to see a ghost?" When they enter that page, they and the room they are in seem to reflect on that page as if it were a mirror. Mattie will get terrified because there are some net creatures (They are a kind of greenish-grey cyberfigures, called "ghosts", and there are many of them).
People get affected when they watch the strange webpage, and before long, people commit suicide or become a heap of dust. Mattie realises that there are less and less students on the campus, those few who still go to university are silent and keep to themselves. Nobody wants to talk about what's happening. She specially misses her friend Isabelle Fuentes (Christina Milian), who is attacked by several of them going out of a laundry machine.
At that moment is when Mattie starts to really believe that there is a threat. Mattie realises that Douglas had bought a computer second-hand. Dexter (Ian Somerhalder) was the original owner. At first, he doesn't want to have anything to do with Mattie's problem, but then he realises that something terrorific is going on. Together, they devise a plan to use a virus developed by Josh (Jonathan Tucker), put it in the network to shutdown the system and save human high-tech way of life.
Josh has imprisoned himself inside his apartment, wrapping everything in red tape, the only thing which seems to prevent the beings from entering places. He's frantic, but finally tells Mattie and Dexter that Douglas and him were working on a project to create the widest possible net connection. Suddenly, all kind of unknown virus have started to appear, and they couldn't turn the computer off. Josh refuses to leave what he considers a safe place.
However, he'll die as well, because the cyber-creatures enter through the main door peephole in the one second he peers outside. Mattie and Dexter got what they were looking for: the virus Josh and Douglas had invented. They need to use it in the centre of the system, in a modem located in the basement of Douglas' building. They are threatened by hundreds of different-looking cyber-creatures on their way there. Mattie is caught by one of them, who steals her wish to fight and live.
She appears surrounded by millions of grey arms. Dexter pulls her out, telling her not to look into the ghost's face. Mattie will wake up unharmed, but she says that the cyber-creature don't belong to the system. "They are the system." They finally find the main server, and they pour the virus into it. However, the system reboots itself, opening the gate to our world once again. Dexter and Mattie run away, get on a car and leave the now empty-streeted city.
All mobile phone networks, net connetions, TV channels have been infected. Only an army-broadcast radio-based message is still working, telling them to go to a refuge out of town. They sleep inside their own car, hoping to get somewhere where there is no net connection or mobile phone coverage.
They are last attacked by a four-armed creature until they reach such place. Later, when they are on their own, they realize they will have to live in the countryside for the rest of their lives without any of the modern technology they'd taken for granted until then.
The movie closes with a voiceover from Mattie where she has come to understand that humanity must retrogress to a lifestyle they had considered primitive, and the ghost-beings have taken over the cities and electronic networks... both groups of beings grimly determined to survive.