Threat Description

Flea

Details

Aliases:Flea, FleaJS/Flea,VBS/Flea.A.Dropper, REG/Flea
Category:Malware
Type:Worm
Platform:JS, VBS

Summary



JS/Flea.A is a slow email worm that operates as a signature in an HTML formatted mail. To hide itself and to make analysis more difficult, Flea uses several encryption layers.



Removal


Automatic action

Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.

More

You may wish to refer to the Support Community for further assistance. You also may also refer to General Removal Instructions for a general guide on alternative disinfection actions.



Technical Details



F-Secure has received reports of this worm from Asia and Europe.


Variant:Flea.A, JS/Flea.A, VBS/Flea.A.Dropper, REG/Flea.A

Flea activates when an infected email message is opened. At this point, the worm connects to a web site in Spain (a private page under terra.es), and silently downloads and executes a JavaScript code available in a web site. This JavaScript code will download an another script written in Visual Basic Script and execute it. This code will contain the actual worm code.

The Visual Basic script code changes Internet Explorer settings so, that any URL entered into address bar without a specific protocol prefix (usually "http:" part in the beginning of the URL) will be directed into worm code, causing that the system will be reinfected.

The worm also attempts to add a number of buttons to Internet Explorer with labels "SEARCH", "ANTIVIRUS", "PILLS" and "SECURITY". Selecting any of these buttons will cause the worm to reinfect the system.

The worm drops two files into Windows installation directory, "c****" and "c****.htm" where **** is a number based on the current date. These first file contain the changes made to the registry and the second file contains the actual signature file used by the worm.

Finally the worm will alter the signature and stationary settings of both Outlook Express 5.x and 6.x. After this all email messages sent from an infected system will contain the hidden link to the worm code.



Detection


F-Secure Anti-Virus detects JS/Flea.A with the update released on October 21st, 2003:
Detection Type: PC
Database: 2003-10-21_02



Description Created: Mikko Hypponen, October 23h, 2003
Technical Details: Katrin Tocheva and Sami Rautiainen, October 23h, 2003


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