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    Earlier the other day, I was browsing through the Yahoo! PH site and the Yahoo! Purple Hunt 2.0 ad caught my attention.

    Curious, I clicked the ad and found my browser downloading a suspicious file named com.com.

    Apparently, this ad redirected me to a randomly generated URL similar to the following, which unfortunately led to the malicious download:

    • hxxp://want6.{BLOCKED}.com/se/3da19bea8f9c03e96c9b1acad9cce5a88a2244f0a34d69
      c09b8d3198b2797726789be0228c0df3c762ed088a2327b07f4a183fa6fa753b0acfd7f0afc2d2b
      13b801ba978269fcda413f53e/960b0a2a/com.com
    • hxxp://nose8.{BLOCKED}.com/se/3da19bea8f9c03e96c9b1acad9cce5a88a2244f0a34d69c
      09b8d3198b2797726789be0228c0df3c762ed088a2327b07f4a183fa6fa753b0acfd7f0afc2d2b
      13b801ba978269fcda413f53e/960b0a2a/com.com
    • hxxp://letter6.{BLOCKED}.com/se/3da19bea8f9c03e96c9b1acad9cce5a88a2244f0a34d69c0
      9b8d3198b2797726789be0228c0f3c762ed088a2327b07f4a183fa6fa753b0acfd7f0afc2d2b13
      b801ba978269fcda413f53e/785c08d8/com.com

    Below is a screenshot of the file download dialog box.

    The downloaded file is detected by Trend Micro as TSPY_PIRMINAY.A. Let’s see how the download took place.

    First, the download only happens once per browser. This means that the malvertisement may have used an IP and user agent filtering process of some sort to prevent multiple downloads, which would make it suspicious to the end user.

    To be able to replicate the malware download from the compromised ad, we used a browser extension that spoofs browser user agents instead of installing different browsers.

    It appears that the advertisement is first redirected to the malware download before it finally brings the browser to the real advertising page. The redirection follows this format for the download link:

    http://{varying string}{random number}.{varying domain}/se/{constant string or guid}/com.com

    We’d like to thank the guys over at Yahoo! Ad Security Ops for swiftly acting on our initial report, taking down the malvertisement so it can no longer harm unsuspecting users.





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