The company behind popular air pollution app AirVisual has said it has been the target of a " coordinated attack " , with " abusive and threatening " messages posted on Facebook , as well as the Apple ##oi website and mobile app Store . AirVisual said it came after company data revealed Hanoi was , at times , the world 's most polluted city , prompting it to take down its mobile app and Facebook page . Hanoi 's Environment website recently warned residents to limit outdoor activity .
The company behind popular air pollution app AirVisual has said it has been the target of a "coordinated attack", with "abusive and threatening" messages posted on Facebook, as well as the Apple App Store and Google Play Store. AirVisual said it came after company data revealed Hanoi was, at times, the world's most polluted city, prompting it to take down its AirVisual apps and Facebook page. Hanoi's Environment Administration recently warned residents to limit outdoor activity.