The attack was the latest in a string that have exploited internet advertising networks, which are designed to reach millions of people online
Yahoo shut down the attack but it worked like this. Hackers bought ads across the internet giant’s sports, news and finance sites. When a computer visited a Yahoo site, it downloaded malware code.
The malware hunted for an out-of-date version of Adobe Flash, which it could use to commandeer the computer. Most of the attacks were blackmail sites.
While Yahoo acknowledged the attack, the company said that it was not nearly as big as security researchers were claiming.
“We take all potential security threats seriously,” a Yahoo spokeswoman said in statement. “With that said, the scale of the attack was grossly misrepresented in initial media reports, and we continue to investigate the issue.”
After news of the attack was revealed, Adobe asked users to update Flash so their computers would no longer be vulnerable.
Wiebke Lips, a spokeswoman for Adobe said: “The majority of attacks we are seeing are exploiting software installations that are not up-to-date on the latest security updates.”