The concept of the .DLL File is microsoft's idea, and they are basically files that do things for applications. Lets say I write a calendar application
and I need the program to get today's date every time it opens. I could make a DLL or Dynamic Link Library that would do that for me.
Now this isn't the best use for dll's. It's just an example.
The purpose is to make the actual program (the .exe file) smaller. Various applications can share common DLL file task.
It really saves space and RAM.
So basically a DLL file is an application helper. The application is the boss man and the dll does what the program wants it to do. This sounds
all fine and dandy, but virus and mal ware programmers have figured out ways to use .dll files for there own good.
How rogue programmers use DLL's.
Lets take the example from above, and see how they could use it. The application calls the dll whattimeisit.dll
(this dll doesn't really exist) every time the person opens the app. This application is popular in fact every one has it on there computer.
A rogue programmer could exploit this by writing another dll that opens a hidden .html file on your computer and creates a Pop Up. He names that dll
whattimeisit.dll and somehow replaces the original dll with a hacked dll. So now every time that application calls that DLL trying to get the date,
it instead launches a pop-up window that annoys the hell out of you.
Make sure your DLL files are ok.
It's suggested that 95% of computers have misregistered dll or missing dll files. It's a good practice to check yours for changes