Apple posted this article regarding:
A recent phishing scam has targeted Mac users by redirecting them from legitimate websites to fake websites which tell them that their computer is infected with a virus. The user is then offered Mac Defender “anti-virus” software to solve the issue.
And MacWorld writes:
Online crime falls mostly into four categories:  self-spreading malware (like viruses);  malware that attacks vulnerable Web browsers when you visit a site (drive-by attacks);  malware that tricks you into installing it (like Mac Defender); and  online scams and Web attacks that don’t hack your computer (eBay scams, phishing, search-result poisoning, and so on). Macs are still unlikely to see the first or fully-automated versions of the second. Mac users have always faced the fourth. But as our numbers grow, it’s only natural we will see more of the third.
Also, MacWorld notes, “Intego on Wednesday warned Mac users that a new variant of the Mac Defender Trojan horse doesn’t require that you provide an administrator password during the installation process.”