Can cyber warfare have serious consequences like the Manhattan project or 9/11?

On April 10, 2008 the Homeland Security Secretary Michael Chertoff came up with a speech on the RSA security conference in San Fransciso that there is a threat of having a cyber attack of a magnitude as September 11 attack on the New York’s World Trade Center. This became apparent during the Estonian Cyber war (April 27,2007) when cyber attacks hit the Estonian parliament, Banks, ministries, and many other communication mediums.
Although Chertoff pointed out Estonia as an example, many people believe that the fear comes from the attacks that happened in 2003 to which the US government refers to “Titan Rain” . During these attacks the hackers breached the computers on the Sandia National Laboratories (Department of energy laboratory whose primary mission is to develop and engineer components for nuclear weapons), Lockheed Martin, NASA and Redstone Arsenal.
Michael Chertoff claimed that currently the US doesn’t have a way to monitor all of its networks and by pointing as an example “hackers gaining access to air travel system” the message was that the cyber warfare could cause as much devastation as the Manhattan project and 9/11. The speech delivered at the conference delivered a message that the US Government believes that cyber attacks can be as devastating as some key turning point in history attacks that changed the world.