'Flashback' trojan estimated to have infected 600K Macs worldwide

A trojan horse named "Flashback" that surfaced last year is believed to have created a botnet including more than 600,000 infected Macs around the world, with more than half of them in the U.S. alone.

Russian antivirus company Dr. Web issued a report on Wednesday noting that 550,000 computers running OS X had been infected by BackDoor.Flashback variants of the malware, as highlighted by ArsTechnica.

An analyst for the company later updated the figure to note that the size of the botnet had reached 600,00. He also pointed out that 274 bots are originating from Apple's hometown of Cupertino, Calif.

According to a map released by the firm, 56.6 percent of infected computers are located in the United States. Canada was second with 19.8 percent, followed by the U.K. with 12.8 percent of cases.

Apple released a Java Security update on Tuesday to resolve the vulnerabilities that the malware is exploiting, but not before a number of Mac users had been hit with the malicious software. Oracle first issued a fix for the vulnerability in February.

Security firm Intego publicized the Flashback trojan last September. Some variants of the software were even discovered with the potential to disable anti-malware protections within OS X.

Researchers F-Secure have provided instructions on how to detect and remove the malware.