How to remove 'Yontoo' adware Trojan from your OS X system

A new Trojan lures users to install a Web plug-in that tracks browsing and presents ads. Here's how to remove it.

Security company Dr. Web is reporting on a new adware Trojan attack that is targeting Mac users, where malicious Web sites will trick users into installing a plugin that will track your browsing and display ads to you.

The malware, called "Yontoo," will be first encountered as a media player, download manager, or other plug-in requirement for viewing contents on some maliciously crafted Web sites disguised as sources for file sharing and movie trailers. When the plug-in prompt is clicked, you're redirected to a site that downloads the Trojan installer and requires you to run it. The installer is for a fake program called "Twit Tube," that when installed will place a Web plug-in or extension called "Yontoo" that will run in popular browsers like Safari, Chrome, and Firefox.

When the malware is running, affected systems will be actively tracked for browsing behaviors, and legitimate Web sites will be hijacked with ad banners and other content that attempts to lure you into clicking it.

Safari plug-ins menu
This menu option in Safari will show you the installed plug-ins, which you can review for the presence of Yontoo or any other unwanted plug-ins. Screenshot by Topher Kessler/CNET

The malware appears to be an ad-revenue attempt by the criminals behind it, but if you have recently installed a suspicious plug-in on your system and are seeing bizarre deal links appearing on frequented Web sites, then check your installed plug-ins for any trace of this malware. You can do this in Safari and Chrome by going to the "Extensions" preferences to see if one called Yontoo is present there, but you can also select the "Installed Plug-Ins" option in Safari's Help menu to view information on your plug-ins. For Chrome, copy and paste the URL "chrome://plugins/" into your browser's address field to get to its plug-in settings. In Firefox you can choose "Add-Ons" from the Tools menu to check for extensions and plug-ins.

If you find a trace of the Yontoo plug-in on your system, then although you can disable it in each Web browser, a more-thorough option is to go to the Macintosh HD > Library > Internet Plug-Ins folder and remove the plug-in manually. Additionally, you should check the plug-in folder for your home directory, which can be accessed by choosing Library from the Go menu in the Finder (hold the Option key to reveal the library in this menu if it is missing), and then locate the Internet Plug-Ins folder in here. When the plug-in is removed, quit and relaunch your browsers.

Since Web plug-ins are one method for malware developers to target a system, one thing you can do to help ward off attacks is to get an inventory of your Web plug-ins folders so you know exactly what is in them, and then be able to better investigate any new items placed there. Another similar approach is to set up a monitoring service in OS X that will inform you whenever new items are placed in the Internet Plugins folders on your system. I recently outlined a method for doing this to monitor Launch Agent folders on a Mac, and you can similarly apply this method to the following two directory paths in addition to the Launch Agent paths outlined in the article:

Macintosh HD > Library > Internet Plug-Ins
Macintosh HD > Users > username > Library > Internet Plug-Ins



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