Halfcros

Classification

Malware

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Halfcros, Halfcross

Summary

O97M/Halfcros is a polymorphic VBA macro virus that infects both Microsoft Word 97 documents and Excel 97 spreadsheets.

Automatic action

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.

Suspect a file is incorrectly detected (a False Positive)?

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 detection database 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.

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Knowledge Base

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User Guide

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Contact Support

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Submit a sample

Submit a file or URL for further analysis.

Technical Details

It consist of two parts, a clear text part and an encoded part. The clear text part will take care of decoding the virus code as needed.

The virus activates when an infected document is opened in Word. It disables the built-in macro virus protection and infects the global template. When the global tempate is infected, the virus will infect all opened Word documents.

When the infected document is closed the virus launches Excel. It checks if there is a file called "Book1." in the Excel's startup directory, and if the file does not exist it disables the Excel's macro virus protection via registry. It then creates and infects the "Book1." file.

Within Excel the virus activates when an infected sheet is deactivated. It uses Word to disable Excel's built-in macro virus protection via registry, and it attempts to infects Word's global template. Then the "Book1." file will be created to the Excel's startup directory if it does not exist.

This virus has a non-destructive payload that activates if user opens an infected document in Word between 12:10 and 12:25 on any day when it displays a message box with a title:

Wonder v2.0 by ThE wEiRd GeNiUs

and with a text:

It's time for lunch (UserName)

where (UserName) contains current user name.


Variant:Halfcros.B

This is a corrupted variant that can't infect Excel workbooks.