Category :


Type :


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.


Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note: You need administrative rights to change the settings.

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 ]'