F-Secure Virus Descriptions : Zarma

Zarma is a memory resident encrypted COM and EXE infector. It was found in France during May 1995.

Zarma is a stealth virus that intercepts interrupt 21h's functions 11h, 12h, 31h, 3Dh, 4Eh, 4Fh, 4Ch, and 6Ch to mask its presence on an infected system. The virus hooks int 3 to its own decryption routine. This routine decrypts a second decryptor on the stack.

Once installed in memory the virus also uses int 1Dh, normally a pointer to some video information, as a gateway to call the original int 21h. A new int 1Ch (timer) handler is installed. It plays with the display controller, effectively shaking the picture on a standard VGA machine.

Zarma is also a retro-virus : it is able to deactivate VSAFE, VDEFEND and VWATCH.

The virus contains the following text:

        ZARMA-VIR by T. Power *** Claudia Schiffer Lives !!!..