Max, I reckon you're asking if a dll is still being used by what was once a valid program (or spyware enhanced freeware) and is now an issue. It's not too hard. You can try CCleaner, I've used it it's fairly good at smoking things you want gone that are unused, like shared .dll's etc. or you can go the manual route For CCleaner download http://www.ccleaner.com/ For the manual route I'm just going to post a link here, as I can't really explain it any better and the author is bang on. http://users.iafrica.com/c/cq/cquirke/dllhell.htm Chances are, you've already tried the regedit route and found you can't ditch the little bugger, because the damn thing has loaded itself. The above will let you know what it is, how it's associated and how to nail it if that's your intent.

There is no sure way to tell if a dll is still used. This is because dll files are installed everytime you install any software. Where the dlls are installed on your machine varies, too. However, you can right click on the dll file, click on properties, and click on the Version tab. Look at the values on this tab to see what the dll file was used for. You can also open your registry (Start, Run, regedit) and search for that dll. The registry is HUGE, so it might take some time. It will most likely stop and show you which program accesses that dll file. You have to remember that when it finds a record in the registry, it actually hasn't finished searching the whole registry - so more values may exist. However, not all programs store data in the registry. And, what's more, a program that's been uninstalled may still have data in there. Sometimes the folder the info in isn't even named after the program, but an encrypted MD5 hashcode. But, if you're looking for a way to tell you which programs use it, I'd start there. But if you want to just get rid of some unused dll files, you can automate the task with various registry cleaning tools. Hope that helps.