This buggy virus infects COM files when they are accessed and tries to hide the size increase of the infected files.
It contains this text:
[Yitzak-Rabin 1.00 (c) made by TorNado in Denmark'96]
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.
Nado contains code to activate when the DEL key is pressed on the keyboard. At this time it tries to overwrite the boot sector of the hard drive with the above text. Nado.841 also deletes anti-vir.dat files.
There are several variants, sized between 584 and 841 bytes. Some of these variants overwrite hard drives and corrupt CMOS setup or just delete antivirus program when they are executed. Some of them also infect EXE files instead of COM files. However, the 841 byte variant is the only common variants. Note that the 584 byte variant can not always be succesfully repaired; it corrupts files when infecting.
Nado was confirmed to be in the wild in Denmark in April 1996.