Windows' File Context Menus

I've spent ages today trying to find how to add my own context-menu entry into the Windows Explorer shell. It's shockingly simple, I don't know why the web sites out there have to over-complicate it so much. Here it is in simplified form:

Create a registry entry at

HKCR\*\shell\<unique name>

Where <unique name> is something meaningful to your app, eg "backup". Set the default value for this key to whatever text you want to appear in the right-click context menu for files. Eg. "&Back this file up" (the & defines which character will become the keyboard shortcut on the menu)

Inside of this key create another key named "Command", eg:

HKCR\*\shell\backup\Command

Set the default value of this key to the path to the program you wish to run. You can also use certain parameters such as %1 (the name of the selected file) or %L (the name of the folder the file resides in). Eg

c:\program files\backup\backup.exe "%1"

This works great for me except for one strange thing: When I select multiple files and click on my newly created context menu item it, for reasons unknown, spawns a freeware hex editor I installed the other day. What the...?! Anyone know what's going on there?

HTH