Summary

This is an unusual virus. It infects COM and EXE files normally, but is also able to infect ZIP files: virus inserts a file called CALLFAST.COM to any ZIP file when they are accessed. This file is a BBS advertisment for 'Dementia BBS' and is infected by the virus.

It seems that the virus has been written to faciliate stealing files from a BBS system. Virus checks any ZIP file for a file called REQUEST.IVA. If such a file is found, virus reads a filename list from this file, collects the files, encrypts them and adds them to the same ZIP file as file RECEIPT.IVA.

Dementia does not need external programs to modify ZIP files.

Dementia contains these texts:

        Dementia
        Copyright 1993 Necrosoft enterprises  -  All rights reserved
        I am the man that walks alone
        And when I'm walking a dark road
        At night or strolling through the park
        When the light begins to change
        I sometimes feel a little strange
        A little anxious when it's dark

[Analysis: Mikko Hypponen, F-Secure]