Beware of a company called 7art-screensavers.com. Installing any of their screensavers will install an application called PremierOpinion.
Some of them specify that you must accept with an OK or Accept button that a “market research” program will be installed too. Not all of them do this, but all do install the malware that can scan your files, record user activity and send notice to remote servers. It can also open a back door on infected Macs.
http://bit.ly/cYzr4A will give you the details and the list of screensaver names.
It is not possible to accidentally install these, nor do they install via infected email like on Windows machines. You would have to go to the site and initiate the download.