The 640 byte variant contains the text
(C) MPS-OPC 1991 v3.1
but the 654 byte one claims to be version 3.2. Not yet analyzed.
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.
Variant:MPS-OPC 1.1
A 469 byte version.
Variant:Slow load
Probably the first version - 376 bytes.
Variant:MPS-OPC 4.01
This virus is structurally different, and belongs to a different family, as it only infects .EXE files, but it is probably written by the same authors.