# What Does "rundll32.exe" Do, and Why is it Screwing Up My Computer? **URL:** \ **Category:** Factual Questions\ **Created:** [June 16, 2004, 12:40am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577 "2004-06-16T00:40:28Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![Lissa](https://avatars.discourse-cdn.com/v4/letter/l/85f322/32.png) [@Lissa](https://boards.straightdope.com/u/Lissa)\ **Post date:** [June 16, 2004, 12:40am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577/1 "2004-06-16T00:40:28Z")
I’m running Windows XP. Over the last week, I’ve been having strange problems with my computer. When I’m surfing, I can’t click on any hyperlinks, or the window freezes. I can’t close it, either. If I do a ctrl+alt+delete, it tells me it’s “running.” Sometimes the entire computer freezes and I have to do a manual reboot. Then, last night, I heard the strangest thing. I came into the office to get a book, and the computer was making a rapid “bonk bonk bonk” noise: it’s the sound you get when you try to click on something and Windows won’t allow you to. Since it wasn’t affecting anything else on my computer, I assumed it was an internet problem. I tried deleting my temporary internet files, and then my cookies. It seemed to work for a while, but then it started happening again. A while ago, I tried to do a start+shutdown, and a window popped up saying a program was still running, did I want to end it? The program was “rundll32.exe” I found it using a file search on my computer. The entire file mane is RUNDLL43.EXE-1223F2FD.pf and it says it’s in Windows/Prefetch. What the hell is Prefetch? There’s about a dozen files with the same name, but with a different series of numbers afterward. They’re relatively small files-- the largest is 58KB. My first thought is that it’s a virus of some kind, but Norton Antivirus doesn’t recognize it as such, even with all the updated virus information. I’m getting irritated. _Something_ has posessed my computer, and I’m getting frustrated trying to figure out what to do. Suggestions? Thoughts? Please explain your answer as clearly as possible, for you will be adressing a computer dimwit. ---
**Author:** ![Mr.Blue\_Sky](https://avatars.discourse-cdn.com/v4/letter/m/d26b3c/32.png) [@Mr.Blue\_Sky](https://boards.straightdope.com/u/Mr.Blue_Sky)\ **Post date:** [June 16, 2004, 12:44am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577/2 "2004-06-16T00:44:47Z")
From [here](http://www.answersthatwork.com/): > [@](#): > > Microsoft’s “Run a DLL as an App”. A DLL is a Dynamic Link Library. In layman and [very] simplistic terms a DLL is a portion of a software program which is only used by the main program as and when specific features of the software are used by the end user (for instance the PRINT function in your wordprocessor). The main advantage is that, using this technique, programmers can develop software which does not end up gobbling up memory through the whole program loading in one go, but which instead only uses enough memory for the core functions of the program, with specific features, implemented in separate DLL files, only loaded as and when the end-user decides to use them (ie. The Print DLL will only be loaded into memory when the end-user clicks on PRINT). Another advantage is that the software developers can also have common features which they have implemented across a range of their programs, implemented just the one time as a shared DLL which is used by all that developer’s programs. RUNDLL and RUNDLL32 are the Microsoft Windows programs that need to be used to load DLLs into memory so that they can be used by specific programs or by Windows. > > Recommendation : > First, note that RUNDLL.EXE only exists in Windows 95/98/ME, it does not exist in Windows 2000/XP/2003 – its path is C:\Windows\Rundll.exe as shown on the Tasks tab of The Ultimate Troubleshooter; anything else and you have a virus (see below). RUNDLL and RUNDLL32 do not normally appear in the Task List in Windows. In our experience they tend to appear only when you are already having problems of some sort with your PC, or a particular DLL is either misbehaving, is buggy, or is having problems, such as a Control Panel applet hanging for example. If you see RUNDLL or RUNDLL32 in your Task List persistently then you should be [slightly] worried (see below the other entry for RUNDLL32) – make sure you have good and up‑to‑date antivirus software, boot into Safe Mode, and run a full virus scan on your PC. If you do not have a virus and see either in your Task List, simply leave it alone. We are not sure as to the other times when the real RUNDLL or RUNDLL32 can sometimes suddenly appear in the Task List, but you should leave them alone in most cases provided, again, that you know you do not have a virus. and > [@](#): > > You have one of the W32.Miroot.Worm / W32/Legemer.Worm / W32.HLLW.Sanker viruses (or another virus). YMMV. ---
**Author:** ![Lissa](https://avatars.discourse-cdn.com/v4/letter/l/85f322/32.png) [@Lissa](https://boards.straightdope.com/u/Lissa)\ **Post date:** [June 16, 2004, 1:20am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577/3 "2004-06-16T01:20:07Z")
Okay, if I have a virus, why isn’t Norton catching it? I have all of my virus definitions up to date. Should I delete those files? ---
**Author:** ![Mr.Blue\_Sky](https://avatars.discourse-cdn.com/v4/letter/m/d26b3c/32.png) [@Mr.Blue\_Sky](https://boards.straightdope.com/u/Mr.Blue_Sky)\ **Post date:** [June 16, 2004, 1:30am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577/4 "2004-06-16T01:30:09Z")
> [@Lissa](#): > > Okay, if I have a virus, why isn’t Norton catching it? I have all of my virus definitions up to date. > > Should I delete those files? NO!! Not until you are absolutely sure they aren’t needed. It may not be a virus. If you know how to use msconfig, you can check the start up folder to see what loads into the system when the computer starts up. It may be related to one of those programs. If you go to the website above (click on “Task List”), you can see what each item in your Task List is and (usually) what program it belongs to. It will advise you whether or not you need to have it running. You’d be surprised how much junk you’ll find. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [June 16, 2004, 1:40am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577/5 "2004-06-16T01:40:35Z")
Another cause for such behavior is your hard drive is dying. Trying to read over and over a funky sector on the disk can make a lot of clicking sounds. The “pre-fetch” comes in because that’s what is going on with the disk. It’s try to read ahead the next part of something and having a rough time of it. So: 1. Run a virus scan. 2. Run a disk check including surface test. ---
**Author:** ![Mr.Blue\_Sky](https://avatars.discourse-cdn.com/v4/letter/m/d26b3c/32.png) [@Mr.Blue\_Sky](https://boards.straightdope.com/u/Mr.Blue_Sky)\ **Post date:** [June 16, 2004, 1:42am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577/6 "2004-06-16T01:42:00Z")
If it is the drive, be sure to back up your data and have all of your program disks handy in the event the drive tanks. ---
**Author:** ![Rex\_Fenestrarum](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rex_fenestrarum/32/7265_2.png) [@Rex\_Fenestrarum](https://boards.straightdope.com/u/Rex_Fenestrarum)\ **Post date:** [June 16, 2004, 2:18am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577/7 "2004-06-16T02:18:21Z")
> [@ftg](#): > > The “pre-fetch” comes in because that’s what is going on with the disk. It’s try to read ahead the next part of something and having a rough time of it. Well… maybe. It depends on what your’re saying there. I read what you wrote as “pre-fetch” means he’s having disk issues. I’m not sure where you’re tying XP’s prefetch (note lack of a dash) in with this. Prefetching is a way for XP to “pre-load” all of (or parts of) programs and XP itself so as to increase system performance. The main reason that XP boots faster than Win2k on the same system is because of prefetching. Disk errors and prefetching are unrelated, unless the file happens to be in the Prefetch folder, in which case the app should still load normally (albeit slower than usual). Besides, if he’s using NTFS the MFT should have caught the disk error and moved (or deleted) the bad cluster. **Mr. Blue Sky** : You can delete everything in the Prefetch folder without problem. XP will “re-Prefetch” the files at the next boot. Some programs might seem a bit slower to start, but will run fine and will regain their normal speed once the machine has been rebooted (and XP has rebuilt its Prefetch list). [Cite for all of the above](http://techrepublic.com.com/5100-6270-5165773.html) Lissa, what happens if you open a command prompt and type CHKDSK C: /F ??? (It will probably say the disk cannot be locked for exculsive access and ask if you want the disk checked at next reboot. If so, say yes and reboot. Let me know if CHKDSK finds any errors. ---
**Author:** ![Lissa](https://avatars.discourse-cdn.com/v4/letter/l/85f322/32.png) [@Lissa](https://boards.straightdope.com/u/Lissa)\ **Post date:** [June 16, 2004, 3:20am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577/8 "2004-06-16T03:20:11Z")
> [@Rex Fenestrarum](#): > > Lissa, what happens if you open a command prompt and type CHKDSK C: /F ??? > (It will probably say the disk cannot be locked for exculsive access and ask if you want the disk checked at next reboot. If so, say yes and reboot. Let me know if CHKDSK finds any errors. You guys are going to roll your eyes in disgust, but I don’t know how to get to a command prompt. I could swear that was an option on my old computer’s menu, but I can’t seem to find it on this one. While I was waiting for replies to this thread, I called Dell Support. The tech I spoke to suggested the problem might be caused by spyware and adware. I installed and ran both Ad Aware and SpySweeper.(I had a sneaking suspicion that just using one wouldn’t catch everything, and I was right: the second one I installed found four that the other one hadn’t.) They found dozens of programs which I’ve deleted. It actually seems to be working. So far, anyway. If someone would kindly clue me in on how to run the CHKDSK for Windows Xp, and I’ll see what that turns up. ---
**Author:** ![ZipperJJ](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zipperjj/32/211_2.png) [@ZipperJJ](https://boards.straightdope.com/u/ZipperJJ)\ **Post date:** [June 16, 2004, 3:27am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577/9 "2004-06-16T03:27:12Z")
In XP, go to START- RUN and type “cmd” (without the quotes) and hit Enter. That’ll open a command prompt. Then type CHKDSK C: /F like **Rex** says and report back to him. ---
**Author:** ![Call\_me\_Frank](https://avatars.discourse-cdn.com/v4/letter/c/90ced4/32.png) [@Call\_me\_Frank](https://boards.straightdope.com/u/Call_me_Frank)\ **Post date:** [June 16, 2004, 3:32am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577/10 "2004-06-16T03:32:55Z")
> [@Lissa](#): > > You guys are going to roll your eyes in disgust, but I don’t know how to get to a command prompt. I could swear that was an option on my old computer’s menu, but I can’t seem to find it on this one. Start-Run-type “Command”, click “Ok” is how you get a command prompt…at least in every version of Windows pre-XP (I use WinME, so I’m not overly familiar with XP) ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [June 16, 2004, 3:45am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577/11 "2004-06-16T03:45:35Z")
I encounter RUNDLL when the user has loaded the PC up with every damn thing s/he can find to install in Win 98. Usually a print job locks up and Control ALT Delete shows RUNDLL to be not responding. Canceling it lets the print job run. ---
**Author:** ![Lissa](https://avatars.discourse-cdn.com/v4/letter/l/85f322/32.png) [@Lissa](https://boards.straightdope.com/u/Lissa)\ **Post date:** [June 16, 2004, 4:19am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577/12 "2004-06-16T04:19:46Z")
> [@ZipperJJ](#): > > In XP, go to START- RUN and type “cmd” (without the quotes) and hit Enter. That’ll open a command prompt. > > Then type CHKDSK C: /F like **Rex** says and report back to him. Aye aye, Cap’n! When I ran the chkdsk, it said it found errors. It asked me if I wanted to fix them at next boot, to which I replied yes. I rebooted the computer, and it ran through the check again. Unfortunately, i was called from the room, so I didn’t get to see what happened at the end. When I got back, I was at my normal desktop screen. Should I reun a defragment or any other maintenance tool? Does anyone know of any other good free adware/spyware removal programs? I’ve just downloaded some, but, surprise! you can’t remove what’s found unless you buy the program. Those programs came up with some things the others missed, it seems. ---
**Author:** ![Rex\_Fenestrarum](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rex_fenestrarum/32/7265_2.png) [@Rex\_Fenestrarum](https://boards.straightdope.com/u/Rex_Fenestrarum)\ **Post date:** [June 16, 2004, 4:54am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577/13 "2004-06-16T04:54:19Z")
> [@Call me Frank](#): > > Start-Run-type “Command”, click “Ok” is how you get a command prompt…at least in every version of Windows pre-XP (I use WinME, so I’m not overly familiar with XP) In NT\2000\XP you want to use CMD.EXE, not [COMMAND.COM](http://COMMAND.COM). [COMMAND.COM](http://COMMAND.COM) is the old 16-bit command processor and is only included in NT for DOS compatibility while CMD.EXE is the full 32-bit version. CMD natively uses long filenames while [COMMAND.COM](http://COMMAND.COM) is stuck with the old C:\MYDOCU~1 convention. Also, certain shell apps (like the Resource kit stuff) only run under CMD, so it’s best just to use that instead of COMMAND. **Lissa** if you’re still having this problem after the CHKDSK, I suspect that it might be some kind of spyware. Both [AdAware](http://www.lavasoftusa.com) and [Spybot](http://www.safer-networking.org/) are free and will remove any crapware on your system (I recommend AdAware; note that there are three versions: AdAware Plus and AdAware Professional (not free) and AdAware (free). Make sure you run the “Update” after you install it (to get the latest “spyware definitions” - just like you would with anti-virus software). Running a Disk Cleanup (Start \> Accessories \> System Tools \> Disk Cleanup) won’t hurt and neither would defragging your drive, but neither of these two will fix the problem in question. ---
**Author:** ![Call\_me\_Frank](https://avatars.discourse-cdn.com/v4/letter/c/90ced4/32.png) [@Call\_me\_Frank](https://boards.straightdope.com/u/Call_me_Frank)\ **Post date:** [June 17, 2004, 3:32am UTC](https://boards.straightdope.com/t/what-does-rundll32-exe-do-and-why-is-it-screwing-up-my-computer/250577/14 "2004-06-17T03:32:37Z")
> [@Rex Fenestrarum](#): > > In NT\2000\XP you want to use CMD.EXE, not [COMMAND.COM](http://COMMAND.COM). [COMMAND.COM](http://COMMAND.COM) is the old 16-bit command processor and is only included in NT for DOS compatibility while CMD.EXE is the full 32-bit version. CMD natively uses long filenames while [COMMAND.COM](http://COMMAND.COM) is stuck with the old C:\MYDOCU~1 convention. Also, certain shell apps (like the Resource kit stuff) only run under CMD, so it’s best just to use that instead of COMMAND. D’oh! Actually, that kinda sounds familiar, so I may have known that longa go and forgotten it… 😃 And if I may be so bold as to add something to **Rex** ’s comment… I’d recomend that you go through the help files to set up the Custom Scan instead of just doing the “Smart System Scan”. The download page on Lavasoft’s site tells you what to do…(What I’m referring to is found under the “Before you start” article in the “Getting Started” category, IIRC)