Virus Name: Tequila
V Status: Common
Discovered: April, 1991
Symptoms: .EXE growth; master boot sector modified; file allocation
errors; decrease in total system and available memory
Eff Length: 2,468 Bytes
Type Code: PRtEX - Parasitic Resident .EXE & Master Boot Sector Infector
Detection Method: ViruScan, F-Prot, Sweep, NAV, PCScan, ChAV,
IBMAV, AVTK, NAVDX, VAlert,
NShld, LProt, Sweep/N, Innoc, AVTK/N, NAV/N,
Removal Instructions: F-Prot, or delete infected files and
replace master boot sector
The Tequila virus was isolated in April, 1991. It is originally
from Switzerland, and at the time of its isolation was thought to
be common in Europe. Tequila is a memory resident master boot sector
(partition table) and .EXE file infector which uses a complex
encryption method and garbling to avoid disassembly and detection by
using a scan or search string.
The first time a program infected with Tequila is executed on a
system, the virus will check to see if it has already infected the
hard disk master boot sector. If the master boot sector has not been
previously infected, Tequila will write an unencrypted copy of
itself to the last six sectors of the system hard disk, as well as
modify the hard disk master boot sector so that it will be
infectious. Tequila will not install itself memory resident at
this time, and it will not infect programs.
Later, when the system is rebooted from the system hard disk,
Tequila will become memory resident. It will be located at the top
of system memory but below the 640K DOS boundary. Interrupt 12's
return will be moved, preventing the virus from being overwritten
in memory. Interrupts 13 and 21 will be hooked by the virus. Total
system memory and available free memory, as indicated by the DOS
CHKDSK program, will be 3,072 bytes less than expected.
After Tequila is memory resident, it will infect .EXE programs when
they are executed. Infected .EXE programs will increase in size by
2,468 bytes, but this increase will not be able to be seen in the
DOS disk directory if the virus is memory resident. The virus will
be located at the end of infected programs. The infected program's
date and time in the disk directory will not be altered.
The following text will be able to be found on the last few sectors
of the hard disk on infected systems. This text is encrypted in
"Welcome to T.TEQUILA's latest production.
Contact T.TEQUILA/P.o.Box 543/6312 St'hausen
Loving thought to L.I.N.D.A.
BEER and TEQUILA forever !"
Systems infected with Tequila will notice file allocation errors
being detected with the DOS CHKDSK command when the virus is memory
resident. If CHKDSK is executed with the /F option, program
corruption may result.
Anti-viral programs which perform CRC checking may not be able to
detect Tequila on files, regardless of whether the virus is memory
Tequila activates four months after the initial date of infection
of the system hard disk. At that time, and every month thereafter
on the anniversary date, the virus will display a graphic and the
"Execute: mov ax, FE03 / int 21. Key to go on!"
If the user executes a program containing this sequence of
instructions, the message which was found on the last sectors of
the system hard disk will be displayed.