Autumn (Leaves) Virus

Alias:Blackjack, 1704, Herbst(laub), Cascade A-Virus
Strain:Cascade- = Autumn- =Herbst-Virus
detected when:September 1988
where:University of Konstanz, FRG
Classification:Program Virus (extending .COM), RAM resident
Length:.COM filelength increases by 1704 byte


Operating System(s):MS-DOS
Version/Release:2.xx upward
Computer model(s):IBM-PC, XT, AT and compatibles


Easy identification:---

Type of Infection:

System: is infected if the call of interrupt 21h with function 4Bh and subfunction FFh is possible and without error and 55AAh is returned in DI- register. .COM file: Program virus, increases COM files by 1704 Byte. A .COM file is infected if the first instruction is a three byte jump with DISP16 = (filelength minus viruslength). .EXE file: no infection.

Infection Technique:
Infection Trigger:Infects all files that are loaded via the function 4Bh and subfunction 00h of the interrupt 21h (MS-DOS uses this function to start any program)
Storage Media affected:
Interrupts hooked:Int21h, Int28h (only if Clockdevice Year = 1980), Int1Ch (only if damage is triggered)
Encoding Method:
Damage:Transient Damage: Modifies screen by making the characters on the screen "fall down" on the screen in connection with clicking noises.
Damage Trigger:IF function GetDate returns with 1. ( year=1988 AND month>= 10 ) OR 2. ( year=1980 AND 2.1. clock is changed by user to year=1988 month>=10 OR 2.2. clock is changed by user to year>1988 ) AND a random number generator activates damage.
Particularities:1. If the system is _not_ infected, the invocation of an infected program produces errors (system crash is possible). 2. COM-files up to a length of 63800 bytes will be infected, but files with a length of more than 63576 bytes are not loadable after infection. 3. The virus-program is encoded, dependent of the .COM-filelength. 4. The distinction between .EXE and .COM files is made by testing the "magic number (MZ)" in the .EXE-Header.


Countermeasures:ANTIHBST.EXE is an antivirus that only looks for the HERBST-virus and, if requested, will restore the file.
Standard means:---


Location:Virus Test Center, University Hamburg, FRG
Classification by:Michael Reinschmiedt
Documentation by:Michael Reinschmiedt Morton Swimmer
Date:July 15, 1989
Information Source:

(c) 1996 Virus-Test-Center, University of Hamburg