Security firm Symantec previously estimated that the authors of the Flashback malware that affected hundreds of thousands of Macs at its peak could have been generating up to $10,000 per day by hijacking users' ad clicks. Further analysis from the company suggests that the developers may have only earned $14,000 over the three weeks the malware was active.

From our analysis we have seen that, for a three-week period starting in April, the botnet displayed over 10 million ads on compromised computers but only a small percentage of users who were shown ads actually clicked them, with close to 400,000 ads being clicked. These numbers earned the attackers $14,000 in these three weeks, although it is worth mentioning that earning the money is only one part of the puzzle—actually collecting that money is another, often more difficult, job. Many PPC providers employ anti-fraud measures and affiliate-verification processes before paying. Fortunately, the attackers in this instance appear to have been unable to complete the necessary steps to be paid.

It is estimated the actual ad-clicking component of Flashback was only installed on about 10,000 of the more than 600,000 infected machines. In other words, utilizing less than 2% of the entire botnet the attackers were able to generate $14,000 in three weeks, meaning that if the attackers were able to use the entire botnet, they could potentially have earned millions of dollars a year.

Symantec notes that the malware developers displayed more than 10 million hijacked ads and could have delivered many more if the developers had been more successful in their attacks.

Some security specialists have said that the Mac OS is "really vulnerable" to further infections, though these claims should perhaps be taken with a grain of salt -- those security specialists make their living off vulnerabilities and it is in their best interest to promote awareness of them.

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