Summary
Zhymn is a dangerous memory resident Win9x virus about 20K in length, and written in Assembler. The virus infects PE EXE files, by writing its code to the middle of a file.
Removal
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.
Technical Details
The virus has many routines that perform different actions: it infects .EXE and .SCR Windows applications; adds infected files to RAR and ZIP archives; patches anti-virus files and memory resident monitors; performs anti-debugging tricks, etc. The virus also has a very complex programming style.
When an infected file is run, the virus infects the EXPLORER.EXE and WSOCK32.DLL files in Windows directories, infects Windows executable files in the Windows and PATH directories, and then the Windows applications that are referred in the Windows registry, then processes directory trees on all local and network drives and infects Windows EXE files in them as well. The virus then stays memory resident, and infects EXE files that are accessed. The virus also creates its "pure dropper" in the Windows directory with a KERNEL.EXE name, and registers this file in the system registry in the auto-run section:
Software\Microsoft\Windows\CurrentVersion\Run
While infecting WSOCK32.DLL, the virus hooks its three functions: "recv", "send" and "connect", which is similar to email worms.
The known version of the virus does not send itself from the computer, but blocks any connection to anti-virus Web sites. The infected WSOCK32.DLL also looks for special packages arriving to an infected computer (special emails), and extracts specially prepared data from them. These data actually should be processed by the virus as executable routines, so the virus seems to obtain and execute so-called "plugins", similar to the method by which the "Hybris" worm operates.
The virus runs itself on January 1st, and plays the hymn of the former USSR.
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