Researchers have found approximately 2% of Macs have been infected by the Flashback malware.
How could this happen? Oracle, who now owns Java after their acquisition of Sun, discovered and fixed 14 security weaknesses in Java on 2/14. These patches were made available to those using the Windows and Linux operating systems at that time. Apple, who controls the update process for Java on Macs, waited until 4/3 to apply the patches. During that 7 week window of vulnerability, cyber-criminals were able to develop a Trojan which exploited over 600,000 of the unpatched Macs. Over half are believed to be in the US.
Am I in the 2%? The security company Kaspersky has provided a way for you to check your Mac to see if it has been compromised and how you can deal with the issue at http://flashbackcheck.com/ .