According to this post at Vital Security, a component of spyware BroadcastPC causes the download and installation of Microsoft's .NET Framework. Being that the Framework is 65MB, this download becomes much more noticeable than the surreptitious advertisement downloads initiated by other spyware. I assume that BroadcastPC engineers started messing around with Microsoft's new programming structure and built a .NET component. But the .NET Framework isn't deployed to all Windows PCs just yet, so a component that needs it might initiate the download as part of Windows update. Also, I found this post by reading Sunbeltblog. This blog is written by staff members of Sunbelt Software, the company that makes iHateSpam and Counterspy, two effective tools to stop spam and spyware, respectively. I've met with some of the people from Sunbelt Software, and I was impressed by their passion for their work.