Rundll32 is a System Utilities software developed by Gerson Kurz. After our trial and test, the software is proved to be official, secure and free. Here is the official description for Rundll32:

EditByMarydown: One day a process was eating up 90% of My CPU time, and its name was RUNDLL32. Arg, I hate that ! That little program is used to start COM objects and other nuisances. So then I patched RUNDLL32 to write its startup arguments to the event log.

Download
This little hack is released as freeware, without any license attached. Use at own risk. Download here (6.241 bytes). You can also download the complete sourcecode (4.740 bytes).
Installation on Windows NT

Just Extract rundll32.exe to your winntsystem32 directory. Maybe you'll want to rename or backup your existing Copy of rundll32.exe, you really should.
Installation on Windows 2000

Installation on Windows 2000 is a bit more tricky because of the stupid "System File Protection" stuff. Here's howto:

Delete RUNDLL32.EXE from winntsystem32dllcache. This is a "master" directory for the winntsystem32 files SFP keeps.
Maybe you'll want to rename or backup your existing copy of rundll32.exe, you really should.
Extract the files from the download archive to winntsystem. You'll get a Warning that rundll32.exe has been replaced, cancel that.
Done.

Note that the first step is vital, otherwise SFP will silently overwrite the patched version. Duh.

Installation on Windows XP
I have no idea, I don't use Windows XP.