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Yahoo ads may have infected thousands with malware; what to do if you're one

Thousands of Windows computer users who clicked on Yahoo ads may have infected their computers with malware.
Thousands of Windows computer users who clicked on Yahoo ads may have infected their computers with malware.
Photo by Justin Sullivan/Getty Images

Yahoo has confirmed that some of its ads over the past week or two delivered malware to those unfortunate enough to have clicked on the ads. The company says it has since removed the offending ads.

If you clicked on a Yahoo ad in the past week or two, you may not know for sure whether your computer has been infected with a virus or other malware. Common symptoms include pop up ads, slow performance and frequent freeze-ups. Some malware can sneak past anti-virus software and hide in the background, recording keystrokes or doing other dastardly deeds, for many months without causing noticeable disruption.

If you think you clicked on a Yahoo ad on your Windows computer during the last couple of weeks, you may want to perform a System Restore, even if you don't notice anything unusual on your machine. Simply clicking on one of the malicious ads was enough to infect a computer in many cases. You wouldn't have necessarily received any dialog boxes or warning messages.

To perform a System Restore in Windows 7, Vista or XP, click the Start Menu or Orb, then All Programs, Accessories, System Tools, System Restore. Follow the prompts, and choose a date two weeks ago. Your computer will restart during the process. A System Restore takes your computer's operating system and programs back in time, but doesn't affect your data files like documents and photos.

If you think you have an infection and want to take a stab at cleaning it before going through a System Restore, SuperAntiSpyware and Malwarebytes offer free downloads to get you started. If they find nothing or can't clean what they do find, you can move on to TDSSkiller and HitmanPro.

TDSSkiller is a free Kaspersky utility for removing a type of malware called a rootkit. HitmanPro is good at finding other types of malware that mainstream anti-virus software programs miss. The free version will find suspected malicious software, but you'll have to do the cleanup yourself unless you buy the full version of HitmanPro.

If you're not that comfortable with digging through the results of the HitmanPro scan and trying to remove the offending files yourself, you may want to strongly consider purchasing the full version to do the work for you.

During manual removal of malware, you may encounter files that won't go away. Windows complains if you try to delete certain files because malware writers intentionally make their unwanted files difficult to get rid of. For removing these files, you can try free tools like FileAssassin or Unlocker.

If one doesn't work, try the other one, since they function differently. If you install Unlocker, be sure to uncheck options for installing the additional software it carries with it, which may not technically be malware but is probably unwanted.

If this article helps you or if you have tips that might help others, please feel free to comment below.