April 1 is the day the Conficker computer worm was supposed to do something terrible to millions of computers running Microsoft Windows -- though engineers were at a loss to say just what that something was.
So what happened? If your computer lets you read this story, we can presume it's not a smoldering wreck.
But somewhere in cyberspace, some hacker, or hackers, created Conficker, and they're still out there. So are others.
Merriam-Webster has multiple definitions of "hacker." One is very positive: "an expert at programming and solving problems with a computer." Another is darker: "a person who illegally gains access to and sometimes tampers with information in a computer system."
But you may be surprised to know what's happened to the most famed hackers of the past. We went looking for a way to measure the top cases -- perhaps in terms of dollar cost or computers infected -- and the consensus we found was that it's hard to do.
"Tagging a damage amount or number of machines compromised to a single virus (let alone a single person) is very difficult," said Nicholas Newman, who tracks computer crimes at the National White Collar Crime Center.
"Data can be transmitted across the globe in a matter of seconds, and computers are infected with malware just as quickly," he wrote in an e-mail to ABC News. "As a result, accurately counting the number of machines infected by a particular worm is impossible and can only be estimated."
Alfred Huger of Symantec, the online-security firm, largely agreed. "We don't track individuals," he said, "we follow software threats."
He named some particularly virulent cases of recent years: the Code Red worm of 2001 and the SQL slammer worm of 2003 (no perpetrators were caught), as well as the Blaster worm from 2003 (an 18-year-old from Minnesota, Jeffrey Parson, served 18 months for writing one variation of it).
He said Conficker is tops on his list in recent years: "It was dramatic in how quickly it moved. However, it didn't have any impact. Yet."
So here are some of the most famous -- or infamous -- hackers, compiled with the help of Symantec, the Justice Department, the National White Collar Crime Center, and several technology consultants. You may despise some of them; others, you may actually like. Please feel free to suggest others, or argue with our choices, in our comments section.
In 1983, Fred Cohen, then a Ph.D. student at the University of Southern California, wrote a short program, as an experiment, that could "infect" computers, make copies of itself, and spread from one machine to another. It was benign. It was hidden inside a larger, legitimate program, which was loaded into a computer on a floppy disk -- something few computers sold today can accommodate anymore.
Other computer scientists had warned that computer viruses were possible, but Cohen's was the first to be documented. A professor of his suggested the name "virus." Cohen now runs a computer security firm.