Fever is an Internet worm that spreads itself as an attachment to
email messages. The worm works under Win32 systems only. The worm
itself is a PE executable about 8 kb long and is compressed with
Petite file compressor.
When the worm attachment is opened, it activates and first checks
if the system is already infected. If not, it tries to copy
itself to Windows System directory with a random name (the name
is generated from a victim computer's name and looks like this
'*32.EXE', for example 'BM32.EXE').
On Windown 9x systems the worm adds a startup key for its file to
the following key in the Registry:
On Windows NT systems the worm uses Service Control Manager to
register itself as a service.
As a result of the above manipulations, Windows will launch the
worm's file automatically at every startup.
The worm uses Windows debugging capabilities to capture
WSOCK32.DLL loading and modifies the beginning of 'send' function
so that it will give control to the worm's code when called. This
way the worm can intercept and analyse the outgoing traffic. It
captures SMTP commands to get the e-mail addresses. Whenever an
email is sent, the worm remembers the sender's and recepient's
e-mail addresses and sends a copy of itself to the recepient of
the previous e-mail.
The infected e-mail message sent by Fever worm looks like that:
The worm's file with .SCR extension is attached to every message.
The worm contains the following text strings:
'[ Yellow Fever BioCoded by GriYo / 29A ]'
'[ Disclaimer: This software has been designed for research purposes only.
The author is not responsible for any problems caused due to improper or
illegal usage of it ]'
[Analysis: Gergely Erdelyi, F-Secure Corp.; May 2001]