WASHINGTON (AP) -- The mysterious caller claimed to be from Microsoft and offered step-by-step instructions to repair damage from a software virus. The electric power companies weren't falling for it.

The caller instructed the companies to enable features in their computers that actually would have created a trapdoor in their networks. That vulnerability would have allowed hackers to shut down a plant.

The incident, documented by one of the government's emergency cyber-response teams, shows the persistent threat of electronic attacks and intrusions that could disrupt the country's most critical industries.

The House this coming week will consider legislation to better defend these and other corporate networks from foreign governments, cybercriminals and terrorist groups. But deep divisions over how best to handle the growing problem mean that solutions are a long way off.