When an infected file is executed, the virus will install itself in memory and hook INT 21h. If the day is 5th of any month, virus will also hook INT 8h (system timer).
Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.
A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:
Check for the latest database updates
First check if your F-Secure security program is using the latest updates, then try scanning the file again.
Submit a sample
After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.
Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.
Exclude a file from further scanning
If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.
Note: You need administrative rights to change the settings.
The INT 21h handler intercepts calls to DOS function 4Bh (load program). If the filename fits "*.COM" it is considered for infection. Only those files that are smaller than 62.5kB and have no EXE 'MZ' header are infected. Files which have the word 1972h at offset 3 are left alone. Nothing is done about changing file attributes so if the virus tries to infect files with read-only attribute, DOS will produce an error message.
If the day was 5th of any month, virus will trigger some time after the execution of an infected program. Depending on the video mode, the virus may cause a scrolling effect on the screen or emit a beep through the speaker.
Virus code contains a text saying 'Signs Of Life !'
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