Though more than 600 million people worldwide use the Internet, it takes only one virus writer to make just about all of us miserable. Like a single stray neutron in a critical mass of plutonium, a lone virus can trigger a chain reaction that spews thousands of copies from desktop to desktop. Last summer's aptly named SoBig virus was an all-too-real example of this danger. "At [SoBig.F's] peak, one out of 17 e-mails that we were processing was a copy of the…virus," says Josh White of U.S.-based e-mail security group MessageLabs. "Certainly we haven't seen numbers like this before." At that time AOL scanned 40.5 million e-mails and found SoBig.F in half of them. In fact, SoBig accounted for 98 percent of all viruses then circulating---all this from a single virus-writing miscreant. How can we possibly hope to stop the inevitable legions of similarly determined troublemakers? Better get used to it: There are no easy solutions to the virus problem.