Jalabed.b is an Internet worm that spreads by e-mail via messages with infected attachments, and through chat networks using the mIRC chat program. The user can accidentally infect a computer by running malicious files attached to malicious e-mails or received from other chat users. Once executed, the parasite installs itself to the system and runs a spreading routine. It gathers e-mail addresses from the Windows Address Book and sends bogus letters to each of them. Jalabed.b also alters the mIRC program’s configuration in order to cause it sending malicious files to other chat users. Furthermore, the worm may propagate through file sharing networks using the Kazaa program. The worm does not carry any destructive payload, as it is designed mostly for spreading. Jalabed.b searches for and overwrites an index file of locally stored web site. The worm runs on every Windows startup.