Cyber security experts report that more than 10 million devices running the world’s most popular smartphone operating system are infected with malware created by a Chinese cybercriminals.

Researchers say the malware, called HummingBad, has generated more than $300,000 a month in “fraudulent ad revenue” for the Chinese hacker group Yingmob.

"Yingmob runs alongside a legitimate Chinese advertising analytics company, sharing its resources and technology," the researchers claim. "The group is highly organized with 25 employees that staff four separate groups responsible for developing HummingBad's malicious components.”

Affected device owners likely have no idea their devices have been infected, and there are currently no tools available to root out the malware once it is installed. This means all infected devices and their data “remain exposed,” according to researchers.

HummingBad is usually installed as a “drive-by download attack,” landing on users’ smartphones or tablets when they visit certain websites. The U.S. has around 288,800 infected devices. A Google spokesperson says they have long been area of the malware and are constantly upping measures to detect it.