What Is An ActiveX Control?

ActiveX is a standard dreamed up by Microsoft so that you can make use of the same code across multiple programs without “re-inventing the wheel” as developers like to call it. ActiveX Controls are an extension on Microsoft’s COM (Component Object Model), which allows for programs to interoperate with each other, so an ActiveX Control that is programmed in C# can talk to other ActiveX Controls that are programmed in C++.
How is this used in practice? For instance, Internet Explorer in its default installation state cannot play flash videos, but with an ActiveX control from Adobe, it can. As you can see ActiveX controls add more functionality to programs.
So What Is Wrong With That?

You might by now be thinking that ActiveX Controls are really helpful, and they are. The problem is that third-party plugins often contain security risks. In Internet Explorer, ActiveX controls can be downloaded and executed in the background and pose a risk of you being infected, via drive-by attack where you go to a website that exploits a security hole.

CREDITS: How to Geek

How to Help Prevent Drive-By Viruses Using ActiveX Filtering in IE9