To run from infected messages the worm exploits the IFRAME security breach.

Installation
The worm copies itself to the Windows System directory under the name "Runouce.exe" and then registers this file in the following registry auto-run key:

 HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
  Runonce = %System%\Runouce.exe

When the Runouce is launched it creates a 'mutex' named "ChineseHacker" to avoid running multiple instances.

Spreading
The worm creates .EML files containing its copy in all available directories, and network resources, excluding the Windows directory. The name of the .EML files is the name of the victim's computer. For example, if the computer name is COMPUTER, the worm creates COMPUTER.EML files in that computer's directories.

Runouce searches for victim email addresses in WAB databases and files with .ADC and R.DB extensions on all available drives except the Windows directory, and sends infected messages to these addresses. To send infected messages, the worm directly accesses the SMTP server "btamail.net.cn".

Other
The Runouce worm searches for files with .EXE and .SCR extensions on all fixed and remote drives, except the Windows directory, and modifies their file access time data.

Runouce also closes programs with some Chinese titles (probably Chinese anti-virus programs).