Google has released its annual Android security report, detailing the steps the company took in 2015 to protect the Android ecosystem, including efforts with Android partners and the security research community. While Google swept up more potential threats in 2015 than before, the company cautions that apps downloaded from sites other than the Google Play Store continue to be a source for malware.

Google reports that every day in 2015, it checked more than 6 billion applications installed on Android devices for potentially harmful apps. It also scanned more than 400 million devices daily for network-based and on-device threats.

Google defines a potentially harmful app (PHA) as one that may harm a device, harm the device's user, or do something unintended with user data through the device. Potentially harmful apps include intentionally malicious apps such as phishing apps and ransomware.

As part of its security efforts, Google worked to make it more difficult for PHAs to appear in the Google Play Store. The company says it reduced the probability of installing a PHA from the app store by more than 40 percent, compared to 2014.

As well as reviewing all applications submitted to the app store, Google says it examined all Android apps it was able to locate on non-Google public websites.

Despite its work, Google says it saw an increase in the number of PHA installation attempts outside of the Google Play App Store. On average, less than 0.5 percent of Android devices had a PHA installed during 2015. Android devices that installed applications only from the Google Play App Store averaged less than 0.15 percent.

Clifford Colby follows the Mac and Android markets for He's been an editor at Peachpit Press and a handful of now-dead computer magazines, including MacWeek, MacUser, and Corporate Computing.