XF ("eXcelFormula") is a general detection for harmful code written with Microsoft Excel's Formulas.
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.
Harmful code found in a Microsoft Excel file will typically be a macro virus.
Macros are sets of instructions that can be triggered by a single command (or even by clicking a button in a program's user interface). Though macros are extremely useful for automating legitimate but repetitive tasks, they can also be misused to perform harmful actions. When used in a harmful manner, they are referred to as macro viruses.
Macro viruses are most commonly associated with Microsoft Office programs (such as Word, Excel or Access), due to their popularity.
An Excel file with harmful code may hide the page containing the code, or use other social engineering tricks to deceive the user into believing it is legitimate or harmless.