A decade ago, most viruses and worms were unleashed by curious students, pranksters and punks wanting to see what kind of damage they could inflict. That quickly evolved into criminals and thieves writing most of the malware once they realized money could be made. Now, governments have arrived for the party. State-sponsored cyberwar is an increasing concern as more and more nations arm themselves with cyber-weapons. Japanese defense engineers, for example, announced that they've developed a digital virus that can track down, identify, and disable attacking systems. Development of the virus began three years ago, and has only been tested on a closed network so far, the Daily Yomiuri reported. The idea of digital viruses being used to thwart ongoing attacks isn't new. Following the infamous Code Red worm in 2001, a number of worms -- Code Blue and Code Green among them -- were released to patch systems that were vulnerable to Code Red infections. Code Green even tried to clean Code Red infected systems. Around 2005, according to reports from experts close to the military, the U.S. government began to significantly invest in the development of programs and exploits robust enough to wage cyberwarfare. The tools range from botnets to software exploits to powerful worms. Today, most large governments are suspected of or have stated that they have put into place offensive cyber-warfare capabilities. Many have speculated that Stuxnet, with or without help from Israel, was a U.S. government creation. "When it comes to nation-on-nation war, automated counter-defenses makes sense," says Pete Lindstrom, research director at Spire Security. "Humans can't match the scaled response computers can achieve." However, if governments start launching large-scale electronic responses to attacks, such as unleashing viruses and worms meant to neutralize an attack, or conducting denial-of-service attacks designed to knock adversaries offline, enterprises had better brace for the potential for collateral damage. "Once released, no one really knows what the impact could have on certain systems and networks." David Mortman, an analyst with the security research firm Securosis, says enterprise security managers need to brace for all of the same types of attacks that we've seen across the past two decades. "It's unlikely you are going to see anything new from viruses, worms, denial-of-service, botnets, software exploits, social engineering," says Mortman. "But you could very well see increased scale. Essentially, to protect yourself from these kinds of attacks, you need to be doing all of the stuff that you should already be doing, and that's to have the right defenses and plans in place for traditional attacks and disasters." George V. Hulme writes about security and technology from his home in Minneapolis. You can also find him tweeting about those topics on Twitter at @georgevhulme.