One might assume Philet0ast3r would favor destructive viruses, given the fact that his apartment is decorated top-to-bottom with anticorporate stickers. But Philet0ast3r's viruses, like those of many malware writers, are often surprisingly mild things carrying goofy payloads. One worm does nothing but display a picture of a raised middle finger on your computer screen, then sheepishly apologize for the gesture. (''Hey, this is not meant to you! I just wanted to show my payload.'') Another one he is currently developing will install two artificial intelligence chat-agents on your computer; they appear in a pop-up window, talking to each other nervously about whether your antivirus software is going to catch and delete them. Philet0ast3r said he was also working on something sneakier: a ''keylogger.'' It's a Trojan virus that monitors every keystroke its victim types -- including passwords and confidential e-mail messages -- then secretly mails out copies to whoever planted the virus. Anyone who spreads this Trojan would be able to quickly harvest huge amounts of sensitive personal information.
Technically, ''viruses'' and ''worms'' are slightly different things. When a virus arrives on your computer, it disguises itself. It might look like an OutKast song (''hey--ya.mp3''), but if you look more closely, you'll see it has an unusual suffix, like ''hey--ya.mp3.exe.'' That's because it isn't an MP3 file at all. It's a tiny program, and when you click on it, it will reprogram parts of your computer to do something new, like display a message. A virus cannot kick-start itself; a human needs to be fooled into clicking on it. This turns virus writers into armchair psychologists, always hunting for new tricks to dupe someone into activating a virus. (''All virus-spreading,'' one virus writer said caustically, ''is based on the idiotic behavior of the users.'')
Worms, in contrast, usually do not require any human intervention to spread. That means they can travel at the breakneck pace of computers themselves. Unlike a virus, a worm generally does not alter or destroy data on a computer. Its danger lies in its speed: when a worm multiplies, it often generates enough traffic to brown out Internet servers, like air-conditioners bringing down the power grid on a hot summer day. The most popular worms today are ''mass mailers,'' which attack a victim's computer, swipe the addresses out of Microsoft Outlook (the world's most common e-mail program) and send a copy of the worm to everyone in the victim's address book. These days, the distinction between worm and virus is breaking down. A worm will carry a virus with it, dropping it onto the victim's hard drive to do its work, then e-mailing itself off to a new target.
