The "Flashback Trojan" malware package, a virus designed to steal personal information, has infected over half a million Mac computers worldwide, BBC News reported.
Many of the infected computers (almost 57 percent) are located in the US, with another 19.8 percent in Canada, CNET reported.
Dr. Web, a Russian anti-virus software company, originally reported that 550,000 Macintosh computers were infected by the botnet.
They later revised the number to over 600,000, with 274 of those based in Cupertino, California, Dr. Web malware analyst Sorokin Ivan tweeted, indicating that the virus was spreading rapidly.
@mikko, at this moment botnet Flashback over 600k, include 274 bots from Cupertino and special for you Mikko - 285 from Finland
— Sorokin Ivan (@hexminer) April 4, 2012
However, the chief researcher at F-Secure, the antivirus firm that warned Mac users about the malware attacks on Monday, was unable to confirm Dr. Web's numbers, ComputerWorld reported.
@sawaba Can't confirm or deny the half a million estimate by Dr. Web. We don't have good stats on Mac malware.
— Mikko Hypponen (@mikko) April 4, 2012
The Flashback virus was first discovered by anti-virus experts in September 2011, Mashable reported. It was initially designed to resemble an Adobe Flash Player installer, but would seek out user names and passwords stored on your Mac once installed. Here's how to find out if your Mac is infected.
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Later versions of the botnet exploited weaknesses in Java programming language, and allowed the virus to be installed from certain websites without the user's permission, BBC reported.
"By introducing the code criminals are potentially able to control the machine," Dr. Web's chief executive Boris Sharov told the BBC. "We stress the word potential as we have never seen any malicious activity since we hijacked the botnet to take it out of criminals' hands. However, we know people create viruses to get money."
Apple released its' own security update on Wednesday to protect Mac users against the virus. It can be activated by clicking on the software update icon in the computer's system preferences panel, BBC reported.
Other security companies have suggested that users disable the Java plug-in in their browsers altogether if they don't use Java-based Web applications, according to CNET.
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