One might assume Philet0ast3r would favour destructive viruses, given the fact that his apartment is decorated top to bottom with anti-corporate stickers. But his viruses, like those of many malware writers, are often surprisingly mild things carrying goofy payloads. One he is 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 email 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, hunting for new tricks to dupe someone into activating a virus. ('All virus-spreading,' one virus writer said caustically, 'is based on the idiotic behaviour of the users.')