Very interesting article Ping.
Another interesting snippet:
"Hundreds of Defense Department computer systems had been penetrated by an insidious program known as a "trojan," the alert warned. "These compromises ... allow an unknown adversary not only control over the DOD hosts, but also the capability to use the DOD hosts in malicious activity. The potential also exists for the perpetrator to potentially shut down each host."
IOW -- they get in, spy on what we have, and can even shut down the computers, or take them over.