SAO PAULO, Brazil — A massive 2007 electrical blackout in Brazil has been newly blamed on computer hackers, but was actually the result of a utility company’s negligent maintenance of high voltage insulators on two transmission lines. That’s according to reports from government regulators and others who investigated the incident for more than a year.

In a broadcast Sunday night, the CBS newsmagazine “60 minutes” cited unnamed sources in making the extraordinary claim that a two-day outage in the Atlantic state of Espirito Santo was triggered by hackers targeting a utility company’s control systems. The blackout affected 3 million people. Hackers also caused another, smaller blackout north of Rio de Janeiro in January 2005, the network claimed.

Brazilian government officials disputed the report over the weekend, and Raphael Mandarino Jr., director of the Homeland Security Information and Communication Directorate, told the newspaper Folha de S. Paulo that he’s investigated the claims and found no evidence of hacker attacks, adding that Brazil’s electric control systems are not directly connected to the internet. Read the full story