Fax Free is a resident file virus, which infects EXE files which are either opened or executed. The virus is 1024 bytes long, of which 787 bytes are encrypted starting at offset 73. After every encryption or decryption virus compares one byte of its code with its unencrypted value. If this byte is wrong when expected right or right when expected wrong, the crypt loop is repeated (paranoid programming). Infected files contain the date when infection has happened.
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.
Virus doesn't infect any files executed from floppy disk. Also, if the file begins with 'AN' or 'LD', it will not be infected. Before infecting any files, the virus calculates two bytes from the file code - if they add up to 255, virus considers the file is already infected and doesn't infect it. Virus infects files only if they're smaller than 512 kB.
Virus checks the system date when an infected file is executed. If the date equals to 25th or 26th of the month, the machine is crashed. Crashing the machine is done by filling 10 bytes of memory at 0000:0522 with 60h.
Virus contains two text messages. The first one is encrypted but the another one, 'Mosquito', is visible in infected files. The encrypted text says
Hello this is the core Rev 3 26/4/91 P 0.98c P. 0.98 Rev 4 24IX89 bye bye
Variant:Topo,Pisello
Two variants, 1536 and 1024 bytes, which have not been analyzed yet.