Perrun is a proof of concept virus that appends itself to JPEG files. In order to run the viral part it modifies the JPEG handler program in the registry and drops a special extractor to the system that extracts and runs the malicious code. In practice it means that the malicious part in a JPEG file will run only if the system is already infected with the virus. A clean system can not get infected from an "infected" JPEG file since that would need the virus to be active on the system already.
Please note that Perrun can not be activated from infected JPEG files on a clean system.
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 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.
The virus modifies local files only. It has no ability to send itself in email or over local network. It has not been reported in the wild yet.
Perrun was written in Visual Basic and it is compressed with the UPX EXE compressor.
When the virus is started in it's EXE form it drops two files:
'extrk.exe' - the program that extracts the virus code from the JPEG files
'reg.mp3' - registry file that adds the extractor program as the handler for opening JPEG files
After this it looks for '*.jpg' files in the current directory and appends itself to them. It does not tuch the file if it has 'alco' as the four last bytes. This way it does not append itself to a file twice.
Since from here the JPEG files are opened with the special extractor the viral code can be started from the JPEG files. The extractor extracts the virus code to 'x.exe' in the current directory and runs it. After that the JPEG file itself is opened with the original handler.