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According to Lookout, the apps used certain software that had the ability to covertly siphon people's personal data on their devices without alerting the app makers.
The impacted apps included mobile games for teenagers, weather apps, online radio, photo editing, education, health, fitness and home video camera apps.
The researchers discovered that the 'Igexin' advertising software development kit (SDK) embedded in the apps caused these to communicate with outside servers that had earlier spread malware.
The bug in SDK was discovered when an app appeared to be downloading large, encrypted files from those servers.
Many of the developers of the impacted apps were unaware of the security flaws, the report added.