Most of the non-malicious spam that we see in search results relates to fake search engines. The operators of these sites make money by tricking users into clicking on disguised advertising. Another way they make money is to convince users to install adware onto their computers as they will then receive a fee from the adware vendor.
For example, LoudMo is a well-known adware vendor. Their affiliate network pays $1.50 per installation.
LoudMo's adversting on their main page
Spammers don't hesitate to trick users into downloading such adware. They hack legitimate web sites to pollute Google search results, and then redirect users to fake video pages.
Fake video
Clicking on the "video" (actually a simple image) warns the user that the "Latest version of FLVDirect Video Player not found! Click OK to install the FREE FLVDirect Video Player latest version."
Prompt to download a video player
The user gets redirected to an external site where he can download the video player. This player is guaranteed "spyware and virus free". This does not mean adware free! 20 antivirus vendors find something dangerous about the executable, 5 flag it as an adware.
Guaranteed "spyware and virus free"!
-- Julien