SAN FRANCISCO (BLOOMBERG) - Facebook Inc. sued two Asia-based developers for allegedly planting malware on Android apps that robotically clicked on ads to inflate revenue.

Through a practice known as "click injection fraud", one of the apps generated more than 40 million ad impressions and 1.7 million clicks through Facebook's Audience Network over a three-month period at the end of last year, according to a complaint filed on Tuesday (Aug 6) in San Francisco federal court.

Facebook has came under intense scrutiny over the use of private data and the impact of harmful content on its more than 2 billion users, with governments around the world challenging its policies. The company, meanwhile, is fighting back against commercial exploitation of its social networks. It is suing firms in China and New Zealand, accusing them of artificially inflating "likes" and "followers" on Instagram accounts.

The developers named in Tuesday's suit are JediMobi Tech Ltd of Singapore and LionMobi Holding Ltd of Hong Kong. JediMobi made the math app Calculator Plus; LionMobi, the utility program Power Clean. Representatives of the firms did not immediately respond to requests for comment.

Facebook alleges the malicious code was installed onto people's mobile phones through the apps.

"At times, the malware was delivered in the form of 'updates' to the apps and, after October 2018, the malware was included directly in the apps," according to the complaint.

Facebook says it discovered the phony ad clicks in December and disabled the apps and banned the developers from the network. It also said it repaid advertisers who paid for phony clicks.

Facebook is seeking unspecified damages and restitution.