Browser Helper Objects, aka BHOs
Browser Helper Objects, or BHOs can be either good or bad, but most of them contain spyware in one form or another. A BHO is sometimes called a toolbar.
Many folks use the Google Toolbar, which is a BHO. When I first installed it, I was given the option to "enable the Google Toolbar's advanced features (e.g., viewing the Page Rank of web pages), the URLs of the sites you visit will automatically be forwarded to Google." I could also decide to turn this feature off later. Google has an extensive FAQ about their toolbar and gives explicit instructions on how to use it, disable or uninstall it. FYI, I don't use the Google toolbar anymore.
There are so many other BHOs out there it would be almost impossible for me to name them all. I used to use one called Hotbar. It allowed me to put a lot of different 'skins' for Internet Explorer, and since I really like my 'eye candy' I thought it was great! Then I found out Hotbar also is spyware. Read what Spyware Guide has to say about Hotbar.
Sometimes these BHOs just sneak onto your computer and you don't even realize they are there! Some of them can be downright malicious!
A majority of the free programs will also install an unwanted BHO unless you watch carefully and uncheck the option to install one of these toolbars.
You can find out if you have any BHOs on your computer in your Startup by downloading and running a real cool little utility called 'WhatinStartup'.
This little gem will also tell you everything else that loads in your Startup! Here's what the website says about WhatinStartup: The WhatinStartup utility displays the list of all applications that are loaded automatically when Windows boots. For each application, additional information is displayed (Product Name, File Version, Description, and Company Name), in order to allow you to easily identify the applications that are loaded at Windows startup.
If StartupRun identifies a spyware or adware program that runs at startup, it automatically paints it in pink color. In addition, you are allowed to Edit, disable, enable and delete the selected startup entries. You can also save the list of startup items into a text or html files, and even add a new startup entry to the Registry.
While you are there, check out the other free utilities there.
Think of BHODemon as a guardian for your Internet Explorer browser: it protects you from unknown Browser Helper Objects (BHOs), by letting you enable/disable them individually. (But it runs at Startup!)