ISTbar
ISTbar is one of the worst malicous programs that you could ever come into contact with! Just like the other programs, it will display advertisements and hijack your web searches. In addition, it can install a toolbar. But the worse part is that advertisements and hijacked web searches will be pornographic.
ISTbar is usually bundled with free toolbars. In addition, just like the others it can be bundled with free softwares or installed using javascript.