Trojan applications are designed to infect smartphones and tablets that run the Android operating system. They turn the devices into a spam-SMS-spewing botnet that can send more than 500,000 texts per day. The malware uses infected phones to silently send out thousands of spam SMS messages without your permission to lists of victim phone numbers. Malware’s creator appears to be monetizing the Trojan by sending gift card spam of the following ilk: “You have just won a $1000 Target Gift Card but only the 1st 777 people that enter code 777 at [redacted] can claim it!””]
Source: https://www.darkreading.com/attacks-breaches/attack-turns-android-devices-into-spam-spewing-botnets