Worm:W32/Downaduprun.A is generic detection of the malicious autorun files created by Worm:W32/Downadup, which exploit the Windows Autorun functionality to spread the worm.
Security programs use generic detections that look for broad patterns of code or behavior to identify similar programs or files. If you suspect the file was incorrectly detected, go to: Removal: Suspect a file is incorrectly detected (a False Positive)?.
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.
Typical Autorun.inf files are very small in size. The Downadup worm inflates the size of its autorun.inf in an attempt to avoid detection by antivirus signature scanners. Binary characters are used to inflate the file size. These binary characters are ignored by the Windows operating system.
On execution of the file, Windows runs the bloated file and finds the following command buried in the garbage text:
This command executes a DLL called jwgvsq.vmx from a hidden folder on the removable drive containing the malicious autorun.inf.
This malware is discussed in the following Labs Weblog post: