How do you know if a smartphone app is legitimate? Thousands of people were duped by a Google Play app that was marketed as anti-virus software, but later found to be useless.

According to the Android Police, Virus Shield doesn’t actually do anything. The app was supposed to scan phones to prevent harmful apps from being downloaded. It didn’t come with annoying pop-up ads and promised to not drain the battery.

The app has since been removed, but not before over 10,000 people bought it for $3.99 per download. Oh, and that 4.7 rating – also bogus.

So how did the fake app make it onto the Google Play Store in the first place? Unlike Apple’s tightly controlled App Store, almost anyone can sell apps in the Play Store with little interference.