From Kaspersky Lab:
Kaspersky Flashfake Removal Tool is a tool to remove this family of malware from your Mac. The first versions of this type of threat were detected in September 2011. In March 2012 over 600 000 computers worldwide were infected by Flashback. The infected computers have been combined in a botnet which enables cybercriminals to install additional malicious modules on them at will. One of these modules is known to generate fake search engine results, displaying false results for users and generating profits for cybercriminals via 'click fraud'. It is quite possible that, in addition to intercepting search engine traffic, cybercriminals could upload other malicious modules to infected computers - e.g. for data theft or spam distribution.