CARA
Alias: 
Strain: -
detected when: 
where: 
Classification: COM-infector, resident
Length: 3 kilobyte(s) + 256 (ORIGINAL paragraph(s)S paragraph(s) FROM TIME OF INSTALLATION)

Preconditions
Operating System(s): MS-DOS
Version/Release: All models
Computer model(s): PC's
Caroname: CARA

Attributes 
Easy identification: 
Type of Infection:
 The virus appends itself to the files Selfrec in memory: Any of Interrupt vectors 61h..64h non-zero Selfrec on disk: File[4] == "CARA"
 
Infection Technique: 
Infection Trigger: (Open || get/set_attr || Load || Rename) &&(4096 <= Filesize < 32767)
Storage Media affected: 
Interrupts hooked: 21/00, 21/3D, 21/43, 21/4B, 21/4C, 21/56, 20, 13/02, 24
Stealth: 
Tunneling/Selfprot: 
Oligo/Polymorphism: -
Encoding Method: 
Damage: Transient: - Permanent: -
Damage Trigger: Transient: - Permanent: -
Particularities: The virus resides above the last MCB Interrupt vectors 61h..64h are used to store the previous vectorsfor interrupts 21h, 20h, 13h and 24h. After infection the file date/timeis read and immediately written again (not sure if this will preserveoriginal date/time). Displayed text: [1] (during install if the value returned by Int 12h isnot divisible by 16) "Virus es en memoria!ClandestinoAuto-ReproductivoAnti-virus", [2] (during floppy boot from installed payload) "Disco es infectado. Reemplaza Boot.ClandestinoAuto-ReproductivoAnti-virus" matching is for ".COM" (case-insignificant) anywhere in the filenamewhich will not always be a .COM file. Int21;ah=0 and Int20 are trappedonce only, to TSR the PSP. Int13;ah=2 is used (1 in 4 times, according toa mod4 counter that counts the following events: sector read operation,bootsector read failed, bootsector successfully written by virus) in orderto check bootsectors of disks in the first 3 floppy drives (when a readoperation is expected) against 6 known bootsector viruses and install thepayload program in the bootsector (108 bytes at offset 7Fh, with an initialjump from offset 0) if one of these 6 is found. Recognises Bootsector[100h]== 1B1h; 6C0h; 0CD00h; 2073h; 2020h; 0C982h. The payload overrides theprevious bootsector program and prints the warning message. If noneof these values is found, the 8 OEM bytes at bootsector[3] are overwrittenwith the (hex) byte sequence 01 34 12 25 12 8C C8 8C
Similarities: 

Agents
Countermeasures: 
Standard means: 

Acknowledgements
Location: Virus Test Center, University Hamburg, FRG
Classification by: Adam David, Frisk Software International
Documentation by: Adam David, Frisk Software International
Date: 28.7.93
Information Source: Caroentry (autom.converter by S.Freitag)