NEW YORK: Google has suspended a number of apps from its Play store following concerns that they were secretly running ads that could not be seen by users and were defrauding advertisers out of an estimated $1bn a year.

The internet giant took action following a report by fraud detection company Forensiq, which warned that thousands of malicious apps were carrying out ad fraud while also severely using up the battery life of devices, Advertising Age reported.

Once installed, these seemingly harmless apps ran in the background, serving thousands of unseen ads and using up to two gigabytes of data.

After monitoring the mobile ad market for 10 days, Forensiq calculated that 1% of all devices in the US ran a suspect app, rising to up to 3% of devices in Europe and Asia.

More than 5,000 mobile apps on both Apple and Android devices were identified by Forensiq as being suspect and it warned they could be costing advertisers at least $857m a year.

It is difficult for advertisers to keep track of the problem because the malicious apps mimic user behaviour and send back seemingly legitimate data. Even if users reboot their phone, these apps can still load in the background.

According to the report, many of the apps were observed generating traffic through most major ad exchanges and networks, establishing 1,100 connections per minute and communicating with 320 ad networks per hour.

Mike Zaneis, executive vice-president and general counsel at the Interactive Advertising Bureau, described the Forensiq report as "groundbreaking".

"It explores the impact in the mobile space when before the focus was on display advertising," he said. "This is the next frontier for criminals. As the money and ad dollars flow toward the mobile space, criminals are going to go there. They are following the money."

Data sourced from Advertising Age, Bloomberg; additional content by Warc staff