F-Secure Virus Descriptions : Fbound

NAME:	Fbound
ALIAS:	W32/Impat.A-mm, I-Worm.Zircon

Fbound is a mass-mailer that was first discovered in March, 2002.

VARIANT: Fbound.C

The Fbound.C variant of the worm appeared in the wild on March 14th 2002.

When activated, the worm first gets user's SMTP server and e-mail address. Then it gets Windows Address Book location, loads up virus exe to memory, encodes it with Base64 encoding, searches WAB file for e-mail addresses and sends itself to all these addresses. The infected e-mail looks like this:

 Subject:      Important
 Attachment:   patch.exe

The message body is empty. When the recipient's address contains '.jp' (Japan) in the end, the subject line is randomly chosen from the list of 16 different subjects.

It should be noted that the worm encodes its file into a single line and this violates RFC regulations for Base64 encoding. So some e-mail servers will not process worm's messages.

The worm doesn't install itself to system. So to remove the worm it's enough to restart an infected computer. After that you can delete the worm's file from temporary folder where it was dropped by e-mail cliend upon attachment execution.

Detection of Fbound worm is available with the updates published on 14th of March 2002.

[Analysis: Gergely Erdelyi, Katrin Tocheva; Sami Rautiainen; F-Secure Corp.; March 14th, 2002]