A BHOo that may not be disabled, at least with the user friendly method in IE6 sp-2. Now all of the malware based on BHO's will use this trick. Way to go Microsoft, just another back door. How many others are there?
You probably forgot that now m$ is making money on removing malware. What do you think one should do to make this business more successful - offer and facilitate OR do not allow and prevent in the first place? -- Keep it simple, it'll become complex by itself...