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