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Uninstallers are notorious for leaving things behind. The question is why, and what you can do about it. The answer: various reasons, and not much.


When I use MS uninstall for an app deletion, such as, Mozilla Firefox I run a search scan only to find a plethora of remaining folders, and registry keys. What does uninstall really uninstall? And how do I safely purge the remaining clutter?

What we have here in front of us is a can of worms.

Uninstallers do uninstall most things, but not everything. Sometimes they could uninstall more, sometimes they should uninstall more, but sometimes you don't want them to uninstall more, and sometimes they can't uninstall more.

Confused yet? Well, that's how the uninstaller would feel, if it had feelings.

On the surface, it seems very simple - an uninstall should remove all files, folders and registry settings that are associated with the program that's being uninstalled.

On the surface.

Let's look at why that's so rarely true.


If you're like me, you probably spend some time customizing the applications you use to your taste. Those settings are likely kept in the registry.

Many applications will leave those customizations in the registry when they are uninstalled, just in case you might re-install the application at some time in the future. After that reinstall you might find all your settings remembered. Yes, an uninstaller could ask, but most do not since it's more work for what most would consider an edge case.

"... uninstalling software is one of the messier, problematic parts of software management."

Quite often also, additional registry entries are created as the program is being used, sometimes not even by the program itself. Unless a program takes special care to keep track of absolutely everything it's created there's no way for the uninstaller to know with certainty everything that should be removed.

So, yes, it's very common that stuff gets left in the registry.

Now the purest might say that the additional work of keeping track, or the additional analysis at uninstall time is worth it, and that all "leftovers" should be removed.

And the purist might well be right.

In fact, the entire genre of registry cleaner applications attempts to fill in this gap. The problem, of course, is that particularly when the application itself can't keep track of what needs to be removed it's nearly impossible to expect a third party application to be able to.

In a very practical sense leaving orphaned entries in the registry doesn't really impact performance that much until or unless it becomes truly overwhelming. And for the vast majority of users that time never actually arrives.

And that's a practical reality that's allowed, and even encouraged, uninstall programs to be careless or sloppy when it comes to the registry.

Shared Files

Most applications include files that can be shared with other applications. For example, Firefox might share some common files with Thunderbird, both Mozilla products. (Not saying that they specifically do, just theorizing an example.)

When you install the first application all required files are installed. When you install the second, those shared files are already there, and may, or may not, be installed or updated.

Uninstall one of the applications. Naturally it cannot uninstall the shared files, or it'll break the other application.

Now, uninstall the second application. What should happen? Ideally it would somehow "know" that the shared files are no longer in use by anyone else and remove them. In reality this is typically a much more complex problem and as a result many uninstallers take the safer approach of leaving behind any files that still might be shared by other programs.

The result is that you might find files and folders on your machine that are no longer in use, simply because the uninstaller chose not to take the risk of removing them, in case some other program was using it. Whether it could have, or should have, or even been able to tell will vary, of course, from scenario to scenario.

Files In Use

It's not uncommon for an application you've installed to have components that are actually running at the time you uninstall it. Whether it's a tray notification application or a system service or something else, it's very common for a portion of the application to be "in use" come removal time.

Once again, ideally the uninstaller would terminate the running component, or ask you to terminate it. Sometimes it does. Sometimes it doesn't. Sometimes it can't, because either the application refuses to terminate, or the uninstaller simply can't know what applications apply or how to "ask" them to terminate.

And as we know, a file that's in use cannot be deleted.

Some uninstallers get around this by asking you to reboot, which forces the application to terminate, and by adding delete instructions that kick in at system boot time. In cases like this, you'll often not see the files actually disappear until you perform that reboot.

Some uninstallers don't even try, and leave the files that were in use behind.

So just what DO they uninstall?


The examples above are just that, examples. Perhaps they are the most common, but there are actually many other reasons that an uninstaller might well leave behind files, folders and registry entries.

So, given all the things that might get left behind, it's a fair question to ask what they do uninstall. What's the short answer?

They uninstall what they can. Mostly.

There's no doubt about it, uninstalling software is one of the messier, problematic parts of software management. Depending on the scenario and the quality of the software, results are often all over the map.

In fact, there's even a term for it: "Software Rot". There are other things that contribute to software rot, but incomplete uninstalls are a major contributing factor.

What to do

My approach is actually pretty simple. Unless I'm experiencing an actual problem that can be traced to or is likely to have been caused by an incomplete uninstall, I do nothing.

Let me say that again: I do nothing.

You can spend a lot of time (and sometimes money) trying to clean up your system, often with little impact on the usefulness or performance of your machine, and often with questionable tools that sometimes themselves cause more problems than they're worth. The practical reality is that incomplete uninstalls are messy but what they leave behind rarely actually causes a real problem.

That being said, the cumulative effect over time does happen. Systems can sometimes become more and more unstable due to software rot depending on how often you install and uninstall software, and what kinds of other things you do with your computer.

I know that there are alternatives that we'll likely hear about in comments to this article, but my position is that the best way to truly clean your system over time is to periodically reformat and reinstall what you do use, from scratch. And I'll even say it's the only definitive and complete way to clean it up.

I do it perhaps every two years, either as a side effect of getting a new machine, repairing a machine, or having a machine finally reach a point where it's the right thing to do.

Article C3646 - February 11, 2009 « »

Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

Gene Thomas
February 11, 2009 1:10 PM

I use revo uninstaller: After it uses the program's built in uninstaller, it then searches for leftover files, directories and registry entries, giving you the option of deleting some, all or none of them. I have always ridded myself of the whole enchalada with no problems. And I install, then uninstall a lot of stuff. Its a disease.

February 11, 2009 1:46 PM

I'm with Leo on this one. Although 3rd party uninstaller software and registry cleaners/tweakers might do the job in a lot of cases, they require your undivided attention to look at everything before a change is made. For an experienced user with a lot of time on their hands, sure, its doable as long as they know what they are doing.

It's safe to assume that a regular uninstall will uninstall the targeted software. Its also safe to assume that you really shouldn't worry what it leaves behind. Ultimately, what can a left behind dll file or log file do to your system if it never opens again after you uninstall the software using it?

The threat of deleting something important is removed by only using the programs uninstaller. Any other method you use is ultimately much more unsafe and not recommended.

If it ain't broke, dont try and fix it!

February 11, 2009 11:14 PM

Revo i use it as well and it is quite harmless anything it removes can be UN done with a a click into system restore. that's right it creates a system restore point. so it is and will be one of the safest apps to use. If you like check it out i will say it again it's safe and it rides the computer of only the left over things that the program left behind. and in a safe whey by creating restore points.

February 12, 2009 12:40 AM

RevoUninstaller it's the best for me!!! I'm using it since a long time and don't dissapoint me. It's free and it let you clean what do you want because it shows a summary before the cleaning process begins. Also take a look at the other options it has like 'autorun manager'.

Good work for the folks of 'Revo'...

Best regards and thanks Leo for your advices.

February 17, 2009 8:32 AM

there is a registry cleaner out there that is safe to run out of the box. as long as it is run under the default settings, it will not do asny damage. i use it and so does several others on my computer help board at aimoo. it is ccleaner. you can get it at leo, try it out and you will see how safe it is. when you run the registry scanner on it, b4 u can fix the problems, it will ask if you want to create a back up of the registry. let me know how you like it........


February 17, 2009 9:36 AM

I use this method (all freeware):

Revo Uninstaller: see comments above

CCleaner: the registry scan actually provides pretty good detail on the items to be deleted.

TweakNow Registry Cleaner: By far the most user friendly registry cleaner.

I agree that it's not necessary to go through all those steps, but it just makes me feel better...kinda like scratching an itch. I also do a complete system restore every 6 months for the same reason. Enjoy!

February 17, 2009 11:21 AM

I learned my lesson, Leo - I got cute with the Revo Uninstaller, reinstalled old apps just to uninstall all traces of them and deleted my system restore in the process. Also, I couldn't click on links in various web pages...Took forever and lots of luck in restoring things to normal (thank heaven I had backed up the registry a few weeks before). Definitely NOT worth the trouble!

Carl R. Goodwin
February 17, 2009 4:56 PM

Reformatting is the ONLY way to go (once a year for me)! :)

February 19, 2009 7:32 AM

I prefer portable programs for this very purpose or "thinstalled" progrms. they don't leave such trail behind. :)

Other than that as mentioned before, reformatting os is the way to go for maintaining performance.

Harold Schulman
February 19, 2009 9:45 AM

I think the "FREE REVO UNINSTALLER" is the best way to go.

February 21, 2009 7:33 AM

Like a lot of the posters said, Revo Uninstaller is one of my top Tools that I use to keep my system clean. The advanced option not only removes leftover files but also cleans the Registry entries for the application you are removing.

I also regularly run registry cleaners like CCleaner, Advanced Windows Care and Eusing Registry Cleaner.

I also reformat AT LEAST once a year, sometimes twice a year. I recommend that ONLY if you know EXACTLY what you are doing and you know you have all your personal files and applications backed up and available for reinstall.

I do enjoy starting out with a fresh install after reformatting because I test a lot of software.

Thanks Leo for a good article!

February 21, 2009 12:06 PM

I do volunteer computer work for my community in New Hampshire. One of my friends led me to this site. I am not a tech professional anymore but have many years of experience fixing, twicking, hacking, building and poking around everything electronics. I have to say I love Leo's "Do Nothing" approach on this one...I happened to share the same opinion. I see a lot of people getting in big trouble for overdoing what does not need to be done. Always back up, reformat every so often and don't forget to K.I.S.S. it :) ! Congrats for a great, really helpful site, Leo.

February 23, 2009 3:23 PM

I use Revo also. I have never EVER encountered a problem using it. But I do have to mention that it also will (at times) leave some files behind. In this case I follow up by searching what I have removed in my PC search engine. I use an app called "Everything" that works EXCELLENT! at finding everything that you type in it's browser. It's really fast too! Just make sure that you are deleting what you really need or have to on the latter. This is what works for me.

Bob Bowen
October 25, 2012 6:35 AM

Thanks Leo, This is the first time I have had a common sense and accurate answer to this problem.

Those who use Revo, think twice. Install the free RegSeeker and type in the exact name (and spaces, if any) and see for yourself that Revo does not do the job of removing dead registry files altogether. If there are no permissions, you are stuck with useless registry files. Sad but true.

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