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.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
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
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.
F-Secure Anti-Virus detects JS/Flea.A with the update released on
October 21st, 2003:
Detection Type: PC
Description Created: Mikko Hypponen, October 23h, 2003
Technical Details: Katrin Tocheva and Sami Rautiainen, October 23h, 2003