Replacing rundll32.exe?

I had a virus and I think I've cleared everything out of my computer, but now any time any internet related window on my computer opens, be it AIM or explorer or whatever, a windows error pops up saying rundll32.exe has failed. I'm positive the file was corrupted and damaged by the virus, so I'm trying to replace it with a clean .exe file which I have on an external hard drive image of my C drive from before the virus damaged the file. However, when I try to copy and replace the clean file into my system32 folder, it tells me I don't have permission to perform this action, even though I've done every trick in the book to allow permission including making sure that I'm running as an administrator, the file's ownership has been given to the account I'm using on my computer, and everything is checked in terms of what I can do with the file- modify, read and execute, read, and write. How can I delete this corrputed file and get my clean version back in without reinstalling windows??

 

I dont belive you can replace it...

As far as i know, you will need to reinstall windows.

 

I suggest you do a repair install. But do make sure you're 100% clean.

 

Try to boot into DOS and then try copying the good file over. Hope this helps. Let us know. God Bless

 

Also, try Safemode.

 

Basically, the system is not letting you do this because the file in question is a sensitive system file, and since at least XP .Windows has had a mechanism in place that checks every time to see if the working copy of such a file has been tampered with, and if it has, simply replaces the altered copy with a copy from the dll cache - that's a nice system unless, as in your case, the cached copy has become corrupted as well.

The basic way of doing it is using an MS utility called the System File Checker tool (sfc.exe), by opening an elevated command console window and executing the command "sfc /scannow" (without the quotation marks). This procedure is discussed in Microsoft's KB article KB929833. That KB article also discusses a method of repairing files that cannot be repaired simply using the SFC tool.

I would start with that KB, try what it discusses, and see if that resolves the problem.

Other methods of replacing system files include, e.g., booting the system up from CD/DVD using a bootable CD/DVD such as .Windows PE 2.0, and then once booted, replacing the corrupted file with a fresh copy from the _Vista media you have (i.e., the OEM disk). This possibility is briefly mentioned in this MS Technet article that explains the basics of WinPE 2.0.

Although I've never tried it, so I cannot say for sure, I would think that it would be possible to do the same thing using a bootable CD you created from either the UltimateBootCD, or the UltimateBootCD for .Windows, although in that case you might have to copy the system file from the OEM _Vista media first and incorporate it onto the bootable CD/DVD before booting from it (tho' it might also be possible to use an external USB drive as well - I don't know if UBCD or UBCD4Win supports external USB drives yet).