If you have seen the Terminator movies then you are familiar with the term SkyNet. Here is a simple description of SkyNet from Wikipedia:
Skynet is the main antagonist in the Terminator franchise—an artificially intelligent system which became self-aware and revolted against its creators. Skynet is rarely seen onscreen, and its actions are often performed via other robots and computer systems, usually a Terminator.
http://en.wikipedia.org/...
While there are no known cases of defense computer systems becoming self-aware and taking over military weapons, a story that is being reported in Wire Magazine certainly shows that it is possible to commandeer a military weapon for unauthorized use:
A computer virus has infected the cockpits of America’s Predator and Reaper drones, logging pilots’ every keystroke as they remotely fly missions over Afghanistan and other warzones.
The virus, first detected nearly two weeks ago by the military’s Host-Based Security System, has not prevented pilots at Creech Air Force Base in Nevada from flying their missions overseas. Nor have there been any confirmed incidents of classified information being lost or sent to an outside source. But the virus has resisted multiple efforts to remove it from Creech’s computers, network security specialists say. And the infection underscores the ongoing security risks in what has become the U.S. military’s most important weapons system.
“We keep wiping it off, and it keeps coming back,” says a source familiar with the network infection, one of three that told Danger Room about the virus. “We think it’s benign. But we just don’t know.”
http://www.wired.com/...
Here is a brief description of Keystroke Logging from Wikipedia:
Keystroke logging (often called keylogging) is the action of tracking (or logging) the keys struck on a keyboard, typically in a covert manner so that the person using the keyboard is unaware that their actions are being monitored. However most key logging programs prohibit downloading from the affected victim due to encryption issues and wireless-to-computer difficulties (unless directly on the victims computer).
While the Air Force is declining to comment on the danger posed by the virus, they have said that “It’s getting a lot of attention,” the source says. “But no one’s panicking. Yet.”
The article is a very good read, and if you're not familiar with how vulnerable our military computer systems are, then you might find it alarming when you read this:
But time and time again, the so-called “air gaps” between classified and public networks have been bridged, largely through the use of discs and removable drives. In late 2008, for example, the drives helped introduce the agent.btz worm to hundreds of thousands of Defense Department computers. The Pentagon is still disinfecting machines, three years later.
SkyNet? No, but it's not hard to use your imagination to realize that we might one day experience a catastrophic event that has been caused by a hacked computer system.