Secunia has issued a Medium risk level for the Zafi.B worm.
It is a mass-mailing worm that sends itself to the email addresses found on an infected computer. It also copies itself to the folders that are likely to be shared on file-sharing networks.
When this worm infects a computer, it attempts to overwrite .exe files. The files that it targets are usually executables that belong to security products. However, in some cases, the worm may overwrite .exe files that belong to other programs.
If the worm does overwrite .exe files, some programs or operating system functions may no longer work correctly.
For more info go to the: Secunia website