| Alias: | --- |
| Strain: | --- |
| detected when: | May 1989 |
| where: | Utrecht (Netherlands) |
| Classification: | Boot sector virus |
| Length: | 512 Bytes |
Preconditions | |
| Operating System(s): | Atari TOS |
| Version/Release: | All versions |
| Computer model(s): | All Atari ST |
| Caroname: | OLI |
Attributes | |
| Easy identification: | If the boot sector is infected, the string "OLI-VIRUS installed ." can be found at end of the boot sector; in memory, the same string can be found at $7B6. |
Type of Infection: | Any boot sector that can be written to. |
| Infection Technique: | |
| Infection Trigger: | Execution of XBIOS disk functions. Execution of boot code. |
| Storage Media affected: | Drive which is set as boot device or accessed by XBIOS. |
| Interrupts hooked: | TRAP #14, TRAP #12 set to old value of TRAP #14. Vertical Blank Interrupt at infection time. |
| Stealth: | |
| Tunneling/Selfprot: | |
| Oligo/Polymorphism: | |
| Encoding Method: | |
| Damage: | Transient damage:1.Message on screen: "OLI-VIRUS installed. " 2. The computer slows down until stop; all CPU time is used by Vertical Blank Interrupt; time until stop depends on the time the computer has been used (=number of VBI's). |
| Damage Trigger: | Internal counter =0 (3rd byte in boot code +$414 in RAM). |
| Particularities: | The virus simulates an uninfected boot sector by modifying the read buffer. The disk information is left unchanged, and the virus code is over- written with $4E ='N'. The virus is recognised by Sagrotan because of direct programming of the FDC. |
| Similarities: | --- |
Agents | |
| Countermeasures: | Make sure that the virus is not in memory. Search bootsector for the string mentioned above. Modify the last byte in boot sector to another value. |
| Standard means: | Clear all bytes in boot sector beginning at offset 30 decimal. |
Acknowledgements | |
| Location: | Virus Test Center, University of Hamburg, FRG |
| Classification by: | |
| Documentation by: | Ronald Greinke |
| Date: | 5-June-1990 |
| Information Source: | |
(c) 1996 Virus-Test-Center, University of Hamburg