Imagine that some malevolent foreign power sent agents to capture people and force them into military service. Further imagine that some of these conscripts were sent out to capture others until the evil regime had amassed an army of millions. What if all that is required to stop these agents of doom is simply lock your door and ask who's there before opening it? Would you take the necessary precautions?

Unfortunately this horrific scenario is being played out right now in cyberspace, and computers are the conscripts. Criminal organizations and even hostile governments are taking control of millions of PCs without their owners' knowledge or consent. Using various forms of malicious software, the bad guys have established armies of zombie machines called "botnets" that stand at the ready to do the evil bidding of their masters.

In January of 2007, one particularly malignant botnet began to form using computers infected with what is now known as the Storm Worm. The infection spread quickly via email and is currently estimated to have recruited between one and ten million PCs in homes, businesses, and government agencies around the world. By some estimates, the total number of zombie systems in all botnets may be as many as 150 million machines.

The Storm Worm botnet has been especially difficult to fight. Most of the time, the infected systems are dormant, merely waiting for instructions. When they do communicate, they do so stealthily using peer-to-peer communication channels rather that via a central server. The creators of the network, or "bot herders," have thus far not been identified, although many researchers believe it is controlled by a criminal enterprise operating out of Russia.

Technically, the code responsible is not a worm in the classic sense. It is a Trojan horse program (i.e., one that masquerades as something else) that is distributed primarily via spam email. The success of the infection depends upon human gullibility and a lack of standard defenses.

In a recent poll conducted by security software maker McAfee and the National Cyber Security Alliance, most users reported having firewalls, antivirus, and antispyware applications installed. Yet when those respondents allowed researchers to scan their systems, between half and one-third of those with the necessary software had not updated or enabled them. If enough computer owners and system administrators would take these simple precautions, the expansion of botnets could be significantly slowed or reversed.

It now appears that the Storm botnet is beginning to segment into smaller networks, with each segment using its own encryption scheme. This may indicate that the bot herders are now ready to sell chunks of their network to other criminal organizations. Should all of these dormant zombies be activated to relay spam or carry out attacks, we may have seen only the leading squall of what could be the perfect storm.