The OS X Flashback malware has become a cash cow for its operations, bringing daily revenues in the thousands of dollars for its perpetrators.
Researchers at Symantec estimated that the nefarious activity of the Mac malware is generating incomes of as high as $10,000 per day in advertising and click fraud.
Symantec reported the malware writers are making a tidy profit from exploiting ad click networks by using the Flashback network of infected systems.
Flashback was able to spread rapidly through OS X systems by targeting an unpatched Java flaw, which Oracle and Apple had left vulnerable for some six weeks.
"This window of opportunity helped the Flashback Trojan to infect Macs on a large scale," the company said in a blog post.
"The Flashback authors took advantage of the gap between Oracle and Apple's patches by exploiting vulnerable websites using Wordpress and Joomla to add malicious code snippets."
Once infected, the malware sets to work monitoring and intercepting web traffic. In particular, researchers have found that Flashback targets the 'GET' and 'POST' calls from the browser as well as search queries.
When users attempt to follow links or search results for certain terms, their systems are redirected by the malware to sites run by third-party affiliates who then pay out ad commissions to the malware operators.
In the process, the otherwise legitimate traffic is hijacked by the infection and used to generate money for the botnet's operators.
While the attack has been seen by some as a watershed event for OS X security, Symantec notes that its methods of generating cash are fairly common for malware platforms.
"Ad-clicking Trojans are nothing new and in an analysis of W32.Xpaj.B last August a botnet measuring in the region of 25,000 infections could generate the author up to $450 per day," Symantec's researchers wrote.
"Considering the Flashback Trojan measures in the hundreds of thousands, this figure could sharply rise to the order of $10,000 per day."
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