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.



From MacRumors:

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.

  Security Firm Symantec Analyzes the Profitability of the OSX.Flashback Botnet