Category: Malware

Type: Worm

Aliases: Fever, Yellow Fever, W32.Yellow.worm, W32/Fever


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.


Automatic action

Based on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the detected program or file, or ask you for a desired action.

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Submit a file or URL for further analysis.

Technical Details

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 email addresses. Whenever an email is sent, the worm remembers the sender's and recepient's email addresses and sends a copy of itself to the recepient of the previous email.

The infected email message sent by Fever worm looks like that:

From: sender@address
To: recepient@address
Subject: pic.gif
[empty body]

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 ]'