Visitors to several popular websites found their computers under attack thanks to malware distributed by two of the largest providers of ads on the Internet.

Among the sites affected were The Jerusalem Post, music streaming site last.fm. But many, many more sites may also be inadvertently distributing the malware.

That’s because the malware has hitched a ride in ads distributed by doubleclick.net (which is a part of google) and ad agency Zedo.  These companies place ads on websites and the sites are paid by the number of people who click. The individual sites don’t select the ads, the ads are provided by the ad placement companies.  Websites trust that legitimate companies like doubleclick.net will screen the advertisers appropriately.

But sometimes ads containing malware can get through. According to the folks at Malwarebytes, they “rarely see attacks on a large scale like this.”

In this case, the actual websites don’t have malware infections. These bad ads send people who click on them to sites that infect their computer with an exploit kit that searches the computer for vulnerabilities and then installs a bot that will then begin to download other malware to the infected computer. So, this is pretty bad news if you get infected.

This particular toolkit is called Zemot and Microsoft updated their Malicious Software Removal Tool to detect it recently.

What can you do? You could do your best to avoid those little ads that pop up on web pages, but how many times have you accidentally clicked on one? The best thing is to make sure you ave adequate anti-malware protection such as Malware Bytes in place.

 ~ Cynthia