Mark works as a System Administrator for uCertify Inc. He has recently installed freeware software from the Internet. He finds that the software displays some advertisements in a corner of the window. He notices that even when he is not downloading anything from the web, downloads are still increasing very frequently, despite the fact he is not using any web browser or Internet applications. After doing some research, Mark finds that the new software is downloading these files. Which of the following types of programs has Mark installed on his computer?