MacDefender showed up on the radar last week as the first fake Anti-Virus (AV) ScamWare for MacOSX. In the Windows world this flavor of malware has existed for years, enticing unsuspecting users into installing bogus AV software under the guise of the client machine being infected. Once it scares you into believing you’re infected, it asks for your credit card information in order to purchase the application that will “fix” the infection. The malware authors hope that this will scare you into purchasing the software.”]
Source: https://blog.talosintelligence.com/2011/05/macdefender-and-its-variants.html