Browser Helper Objects

When an instance of Internet Explorer 4.0 is started, it looks in the registry for CLSIDs stored under the following key:
HKLM\SOFTWARE\Microsoft\Windows \CurrentVersion\Explorer\Browser Helper Objects
If this key exists and there are CLSIDs listed under it, Internet Explorer will use CoCreateInstance() to try to create an instance of each object listed as a subkey under this key. Note that the CLSID of the object you create must be listed as a subkey and not a named value.

For example, imagine that the following entry exists in the registry, HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Browser Helper Objects\{CE7C3CF0-4B15-11D1-ABED-709549C10000}. Internet Explorer will try to create an instance of the object pointed to by the CLSID {CE7C3CF0-4B15- 11D1-ABED-709549C10000} each time Internet Explorer starts.

These registry keys can be created manually or through the self registration portion of your COM application.

There are some requirements when creating a Browser Helper Object

• The application that you create must be an in-proc server (that is, DLL).
• This DLL must implement IObjectWithSite.
• The IObjectWithSite::SetSite() method must be implemented. It is through this method that your application receives a pointer to Internet Explorer's IUnknown. (Internet Explorer actually passes a pointer to IWebBrowser2 but the implementation of SetSite() receives a pointer to IUnknown.) You can use this IUnknown pointer to automate Internet Explorer or to sink events from Internet Explorer.
• It must be registered as a Browser Helper Object as described above.
WARNING: Internet Explorer will create an instance of each Browser Helper Object listed in the registry every time a new instance of Internet Explorer is started. This means that if you have Active Desktop installed, the Browser Helper Objects will be loaded every time you open a new folder as well as when the browser itself is started.