Byder is a worm that spreads through file sharing networks using popular peer-to-peer applications such as Kazaa and Morpheus. Once executed, the parasite displays a few messages asking the user to perform some simple tasks. Meanwhile, Byder installs itself to the system. It creates files with meaningful names in shared folders of installed peer-to-peer clients. It also attempts to delete important files of legitimate software corrupting programs like Yahoo! Messenger, MSN Messenger, Internet Explorer or Notepad, as well as some system components. Byder can reveal itself by displaying a specific message.