Either update Java or turn it off!
Flashback trojan reportedly controls half a million Macs and counting: "Variations of the Flashback trojan have reportedly infected more than half a million Macs around the globe, according to Russian antivirus company Dr. Web. The company made an announcement on Wednesday—first in Russian and later in English—about the growing Mac botnet, first claiming 550,000 infected Macs. Later in the day, however, Dr. Web malware analyst Sorokin Ivan posted to Twitter that the count had gone up to 600,000, with 274 bots even checking in from Cupertino, CA, where Apple's headquarters are located."