Now even YouTube serves ads with CPU-draining cryptocurrency miners

YouTube was recently caught displaying ads that covertly leach off visitors' CPUs and electricity to generate digital currency on behalf of anonymous attackers, it was widely reported.

Word of the abusive ads started no later than Tuesday, as people took to social media sites to complain their antivirus programs were detecting cryptocurrency mining code when they visited YouTube. The warnings came even when people changed the browser they were using, and the warnings seemed to be limited to times when users were on YouTube.

On Friday, researchers with antivirus provider Trend Micro said the ads helped drive a more than three-fold spike in Web miner detections. They said the attackers behind the ads were abusing Google's DoubleClick ad platform to display them to YouTube visitors in select countries, including Japan, France, Taiwan, Italy, and Spain.

The ads contain JavaScript that mines the digital coin known as Monero. In nine out of 10 cases, the ads will use publicly available JavaScript provided by Coinhive, a cryptocurrency-mining service that's controversial because it allows subscribers to profit by surreptitiously using other people's computers. The remaining 10 percent of the time, the YouTube ads use private mining JavaScript that saves the attackers the 30 percent cut Coinhive takes. Both scripts are programmed to consume 80 percent of a visitor's CPU, leaving just barely enough resources for it to function.

"YouTube was likely targeted because users are typically on the site for an extended period of time," independent security researcher Troy Mursch told Ars. "This is a prime target for cryptojacking malware, because the longer the users are mining for cryptocurrency the more money is made." Mursch said a campaign from September that used the Showtime website to deliver cryptocurrency-mining ads is another example of attackers targeting a video site.